Military Jurisdiction

Military Jurisdiction
under the US Constitution, & the concept of

Military Government

(I) Three Kinds of Military Jurisdiction

(II) The Right to Institute Military Governments

(III) Important Clarifications about Military Government

(IV) USMG jurisdiction over SFPT Article 3 and Article 2b cessions

(V) Relevant Supreme Court Decisions

(I) Three Kinds of Military Jurisdiction

The Hague Conventions of 1907 specify that "territory is considered occupied when it is actually placed under the authority of the hostile army." Birkhimer on page 33 of Military Government and Martial Law notes that: "The truth must be that a territory is militarily occupied when the invader dominates it to the exclusion of the former and regular government. The true test is exclusive possession."

The form of administration by which an occupying power exercises government authority over occupied territory is called "military government."

The standard reference for this is Ex Parte Milligan, 71 U.S. 2 (1866), where the Supreme Court held that:
There are under the Constitution three kinds of military jurisdiction: one to be exercised both in peace and war; another to be exercised in time of foreign war without the boundaries of the United States, or in time of rebellion and civil war within states or districts occupied by rebels treated [71 U.S. 2, 142] as belligerents; and a third to be exercised in time of invasion or insurrection within the limits of the United States, or during rebellion within the limits of states maintaining adhesion to the National Government, when the public danger requires its exercise. The first of these may be called jurisdiction under MILITARY LAW, and is found in acts of Congress prescribing rules and articles of war, or otherwise providing for the government of the national forces; the second may be distinguished as MILITARY GOVERNMENT, superseding, as far as may be deemed expedient, the local law, and exercised by the military commander under the direction of the President, with the express or implied sanction of Congress; while the third may be denominated MARTIAL LAW PROPER, and is called into action by Congress, or temporarily, when the action of Congress cannot be invited, and in the case of justifying or excusing peril, by the President, in times of insurrection or invasion, or of civil or foreign war, within districts or localities where ordinary law no longer adequately secures public safety and private rights.

We can organize this more straightforwardly as follows.

There are under the Constitution three kinds of military jurisdiction:

MILITARY LAW is exercised both in peace and war; and is found in acts of Congress prescribing rules and articles of war, or otherwise providing for the government of the national forces;

MILITARY GOVERNMENT is exercised in time of foreign war without the boundaries of the United States, or in time of rebellion and civil war within states or districts occupied by rebels treated as belligerents; superseding, as far as may be deemed expedient, the local law, and exercised by the military commander under the direction of the President, with the express or implied sanction of Congress;

MARTIAL LAW PROPER is exercised in time of invasion or insurrection within the limits of the United States, or during rebellion within the limits of states maintaining adhesion to the National Government, when the public danger requires its exercise; and is called into action by Congress, or temporarily, when the action of Congress cannot be invited, and in the case of justifying or excusing peril, by the President, in times of insurrection or invasion, or of civil or foreign war, within districts or localities where ordinary law no longer adequately secures public safety and private rights.

(II) The Right to Institute Military Governments

See Birkhimer, p. 21
The US Constitution has placed no limit upon the war powers of the government, but they are regulated and limited by the laws of war. One of these powers is the right to institute military governments.

Military Government includes civil administration of military government for interim cessions, which is commonly composed of both civil and military components. Technically speaking, military government is used as an interim and provisional government of undetermined cessions, and especially for "foreign territory" under control by conquest; and while it is not martial law but it can be indefinite; hence the some persons regard military government as the international law equivalent of "martial law."

The administration of occupied territory is conducted under military government. There does not have to be a formal announcement of the beginning of "military government," nor is there any requirement of a specific number of people to be in place, or "on site" before military government can be said to have commenced.

See Birkhimer, p. 25 - 26
No proclamation of the part of the victorious commander is necessary to the lawful inauguration and enforcement of military government. That government results from the fact that the former sovereignty is ousted, and the opposing army how has control. {22}Yet the issuing such proclamation is useful as publishing to all living in the district occupied those rules of conduct which will govern the conqueror in the exercise of his authority. Wellington, indeed, as previously mentioned, said that the commander is bound to lay down distinctly the rules according to which his will is to be carried out. But the laws of war do not imperatively require this, and in very many instances it is not done. When it is not, the mere fact that the country is militarily occupied by the enemy is deemed sufficient notification to all concerned that the regular has been supplanted by a military government.
Reference: {22} Instructions for Armies in the Field, Gi O. 100, A.G. 0., 1863.

Military occupation is conducted under military government, and for Taiwan the United States has delegated the military occupation of Taiwan to the ROC. This is abundantly clear by reading the SFPT, and is explained as follows:
The ROC as an agent for USMG on Formosa is fully apparent under the plain language of the SFPT, (since the ROC did not sign the SFPT, and cannot be considered one of the Allied Powers under the treaty), hence the ROC on Taiwan does not represent the "Allied Powers" nor is it an organ established by the Allies ... but rather the ROC is an agent of USMG, and the SFPT fully recognizes the USA as the principal occupying power.
United States Military Government (USMG) in Taiwan has begun as of October 25, 1945, with the surrender of Japanese troops.

Importantly, the military government of the principal occupying power does not end with the coming into force of the peace treaty, but continues until legally supplanted. This is clarified in the SFPT in Article 4b:
Japan recognizes the validity of dispositions of property of Japan and Japanese nationals made by or pursuant to the directives of the United States Military Government in any of the areas referred to in Articles 2 and 3.
As Birkhimer points out in his Preface to the First Edition published in 1892,
. . . When operating on foreign soil, the legal obligations of the dominant military are tested by one rule; when within their own territory, by a wholly different rule, having regard to the civil and property rights of the inhabitants. What may be permissible to the commander in the exercise of his authority in the former, with no responsibility other than his military superiors, might, in the latter, subject him to grave civil responsibilities . . . .

It is evident, therefore, that there must be one term to express the fact of supreme military domination over the community abroad, and another for the same thing at home.
This is further clarified later in the volume, see Birkhimer, p. 307
Martial law is that rule which is established when civil authority in the community is made subordinate to military, either in repelling invasion or when the ordinary administration of the laws fails to secure the proper objects of government.
The following three quotations are on Birkhimer, p. 1
Military jurisdiction is treated in the following pages in its two branches of Military Government and Martial Law. The former is exercised over enemy territory; the latter over loyal territory of the State enforcing it.

Moreover, military government may be exercised not only during the time that war is flagrant, but down to the period when it comports with the policy of the dominant power to establish civil jurisdiction.

. . . The distinction is important. Military government is thus placed within the domain of international law, its rules the laws of war, while martial law is within the cognizance of municipal law.

Looking back at the period of the Mexican American War in the mid-1800's, the use of the terminology of "martial law" and "military government" were not yet clearly distinguished or separated however. In fact, in today's terminology, the administration of General Scott over the Mexican people was United States Military Government.

(For General Scott's Martial Law Order, Published in the City of Mexico, HEADQUARTERS OF THE ARMY, NATIONAL PALACE OF MEXICO, September 17, 1847, see Birkhimer, p. 339).

For further comments on the nature of military government, see --
Birkhimer, p. 16
Military Government is that which is established by a commander over occupied enemy territory. To entitle it to recognition it is necessary that the authority of the State to which the territory permanently belongs should have ceased there to be exercised.
Birkhimer, p. 21
The erection of such governments over the persons and territory of a public enemy is an act of war; is in fact the exercise of hostilities without the use of unnecessary force. It derives its authority from the customs of war, and not the municipal law. It is a mode of retaining a conquest, of exercising supervision over an unfriendly population, and of subjecting malcontent non-combatants to the will of a superior force, so as to prevent them from engaging in hostilities, or inciting insurrections or breaches of the peace, or from giving aid and comfort to the enemy.
Birkhimer, p. 26
Military government continues till legally supplanted
New Mexico was not only conquered, but remained thereafter under the dominion of the United States. The provisional government established therein ordained laws and adopted a judicial system suited to the needs of the country. The Supreme Court of the United States held that these laws and this system legally might remain in force after the termination of the war and until modified either by the direct legislation of Congress or by the territorial government established by its authority. We have had the same experiences in Cuba, Porto Rico, and the Philippines.
[As referenced above] Birkhimer, p. 1
Moreover, military government may be exercised not only during the time that war is flagrant, but down to the period when it comports with the policy of the dominant power to establish civil jurisdiction.
Winthrop's opus, as quoted in the US Supreme Court case of Madsen v. Kinsella, 343 U.S. 341 (argued Jan. 8, 1952, decided April 28, 1952):
In speaking of the nature of military government, Colonel William Winthrop, in his authoritative work on Military Law and Precedents (second edition, 1920 reprint), says on page 800: "Military government . . . is an exercise of sovereignty, and as such dominates the country which is its theatre in all the branches of administration. Whether administered by officers of the army of the belligerent, or by civilians left in office or appointed by him for the purpose, it is the government of and for all the inhabitants, native or foreign, wholly superseding the local law and civil authority except in so far as the same may be permitted by him to subsist . . . . The local laws and ordinances may be left in force, and in general should be, subject however to their being in whole or in part suspended and others substituted in their stead -- in the discretion of the governing authority."

Also See FM 27-10

362. Necessity for Military Government
Military government is the form of administration by which an occupying power exercises governmental authority over occupied territory. The necessity for such government arises from the failure or inability of the legitimate government to exercise its functions on account of the military occupation, or the undesirability of allowing it to do so. (See para. 12, which discusses military government, and para. 354, dealing with civil affairs administration.)

363. Duty to Restore and Maintain Public Order
The authority of the legitimate power having in fact passed into the hands of the occupant, the latter shall take all the measures in his power to restore, and ensure, as far as possible, public order and safety, while respecting, unless absolutely prevented, the laws in force in the country. (HR, art. 43.)

Taiwan as an area under United States Military Government

At the present time, the United States has many types of overseas territories which are collectively referred to as "the insular areas." All of these areas now have civil governments which handle their affairs, and this is a fact which is so commonly recognized as to scarcely need mention. Indeed, when people refer to US insular areas in the present era, they are referring to areas under "civil government," established by some organic act.

However, what many legal researchers have apparently forgotten is that in the earliest recognition of this concept, all US insular areas were under United States Military Government. We need this recognition before we can discuss the true relationship between Taiwan and the United States.

For those territories over which Spain gave up her sovereignty as a result of the April 11, 1899, Spanish-American Peace Treaty (Treaty of Paris), the landmark ruling of Downes v. Bidwell (1901) introduced the concept of "unincorporated territory" into the United States legal lexicon.

In other words, the US Supreme Court determined that upon the termination of Spanish sovereignty over these territories, under US law they became "US unincorporated territories." However, at the time that the Treaty of Paris came into effect (and indeed for several years thereafter in most cases), all of these territories were under United States Military Government (USMG), and not under any form of "civil government."

Hence, beginning with the Spanish-American War cessions, what the US Supreme Court is speaking of is the category of "unincorporated territory under USMG." Clearly, the three fundamental criteria for the recognition of this most basic type of US insular area are -- conquest by US military forces, the US as "the (principal) occupying power," and territorial cession in the peace treaty. (The issue of whether there is a "recipient" for the territorial cession in the peace treaty is a separate consideration.)

Hence, the earliest recognition of US insular areas included four: Puerto Rico, the Philippines, Guam, and Cuba -- all of which were under United States Military Government. According to the historical record, civil government authorized by the US Congress was achieved on the following dates: Puerto Rico - May 1, 1900; Philippines - July 4, 1901; Guam - July 1, 1950; and Cuba - May 20, 1902.

Cuba became independent on May 20, 1902, but the other three territories continued as US unincorporated territories, each with a civil government in place as of the date indicated. Later the Philippines became independent on July 4, 1946.

CONCLUSION: Under US law, the earliest formulation of a "US insular area" as recognized by the US Supreme Court is the category of "unincorporated territory under USMG."

(III) Important Clarifications about Military Government

Introduction

Military government is the form of administration by which an occupying power exercises governmental authority over occupied territory.

The Hague Conventions of 1907 specify that "territory is considered occupied when it is actually placed under the authority of the hostile army." The form of administration by which an occupying power exercises government authority over occupied territory is called "military government."

Neither the Hague Conventions nor the Geneva Conventions specifically define or distinguish an act of "invasion." The terminology of "occupation" is used exclusively. However, some important clarification is found in US Army Field Manuals.

See FM 27-10

352. Invasion Distinguished
a. Nature of Invasion. If resistance is offered, the state of invasion within any portion of a belligerent's territory corresponds with the period of resistance. If the invasion is unresisted, the state of invasion lasts only until the invader has taken firm control of the area with the intention of holding it. Invasion is not necessarily occupation, although occupation is normally preceded by invasion and may frequently coincide with it. An invader may attack with naval or air forces or its troops may push rapidly through a large portion of enemy territory without establishing that effective control which is essential to the status of occupation. Small raiding parties or flying columns, reconnaissance detachments or patrols moving through an area cannot be said to occupy it. Occupation, on the other hand, is invasion plus taking firm possession of enemy territory for the purpose of holding it.

The Beginning of United States Military Government

Although it seems reasonable to say that the local inhabitants have the right to know that they are being occupied, nevertheless legally speaking, there does not have to be a formal announcement of the beginning of "military government," nor is there any requirement of a specific number of people to be in place, or "on site" before military government can be said to have commenced.

See Birkhimer, p. 25 - 26
No proclamation of the part of the victorious commander is necessary to the lawful inauguration and enforcement of military government. That government results from the fact that the former sovereignty is ousted, and the opposing army how has control. Yet the issuing such proclamation is useful as publishing to all living in the district occupied those rules of conduct which will govern the conqueror in the exercise of his authority. Wellington, indeed, as previously mentioned, said that the commander is bound to lay down distinctly the rules according to which his will is to be carried out. But the laws of war do not imperatively require this, and in very many instances it is not done. When it is not, the mere fact that the country is militarily occupied by the enemy is deemed sufficient notification to all concerned that the regular has been supplanted by a military government.

The Occupying Power

The terminology of "the occupying power" as spoken of in the laws of war is most properly rendered as "the principal occupying power," or alternatively as "the (principal) occupying power." This is because the law of agency is always available.

Explanatory Notes: When the administrative authority for the military occupation of particular areas is delegated to other troops, a "principal -- agent" relationship is in effect.

The conqueror is the (principal) occupying power. This is the clear precedent as established in California, Utah, Nevada, Puerto Rico, Guam, the Philippines, Cuba, etc.

End of Military Government

RULE: Military Government continues until legally supplanted.

This is explained as follows. For the situation where no territorial cession is involved, the military government of the principal occupying power will end with the coming into force of the peace settlement.

Example: (1) Japan after WWII. Japan regained its sovereignty with the coming into force of the San Francisco Peace Treaty on April 28, 1952. In other words, a civil government for Japan was in place and functioning as of this date.

In the situation of a territorial cession, there must be a formal peace treaty. However, the military government of the principal occupying power does not end with the coming into force of the peace treaty.

Example: (1) Puerto Rico after the Spanish-American War. Military government continued in Puerto Rico past the coming into force of the Treaty of Paris of 1898 on April 11, 1899, and only ended on May 1, 1900 with the beginning of Puerto Rico's civil government.

Example: (2) Cuba after the Spanish-American War. Military government continued in Cuba past the coming into force of the Treaty of Paris of 1898 on April 11, 1899, and only ended on May 20, 1902 with the beginning of the Republic of Cuba's civil government.

Hence, at the most basic level, the terminology of "legally supplanted" is interpreted to mean "legally supplanted by a civil government fully recognized by the national (or "federal") government of the principal occupying power."

The Existence of Military Occupation (Military Government) is not a Political Question

See FM 27-10

355. Occupation as Question of Fact
Military occupation is a question of fact. It presupposes a hostile invasion, resisted or unresisted, as a result of which the invader has rendered the invaded government incapable of publicly exercising its authority, and that the invader has successfully substituted its own authority for that of the legitimate government in the territory invaded.

In relation to Taiwan, the "hostile invasion" was aerial bombardment by US military forces.

In Chapter 2 of Formosa Betrayed, author George H. Kerr indicates the beginning of such US aerial bombardment as Thanksgiving Day 1943, and gives further information on bombing raids throughout 1944. In Chapter 2 of Untying the Knot, author Richard Bush also states that US airplanes had begun bombing targets on Taiwan in November 1943. Also see para. 352 Invasion Distinguished.

356. Effectiveness of Occupation
It follows from the definition that belligerent occupation must be both actual and effective, that is, the organized resistance must have been overcome and the force in possession must have taken measures to establish its authority. It is sufficient that the occupying force can, within a reasonable time, send detachments of troops to make its authority felt within the occupied district. It is immaterial whether the authority of the occupant is maintained by fixed garrisons or flying columns, whether by small or large forces, so long as the occupation is effective. The number of troops necessary to maintain effective occupation will depend on various considerations such as the disposition of the inhabitants, the number and density of the population, the nature of the terrain, and similar factors. The mere existence of a fort or defended area within the occupied district, provided the fort or defended area is under attack, does not render the occupation of the remainder of the district ineffective. Similarly, the mere existence of local resistance groups does not render the occupation ineffective.

The military occupation of "Formosa and the Pescadores" (aka Taiwan) began on Oct. 25, 1945 with the surrender of Japanese troops.

The Political Status of Occupied Territory

Military occupation is period of "interim (political) status." The occupied territory is said to be "in interim status under the law of occupation." Since the territory has not reached a final (political) status, it is a sub-sovereign entity.

Explanatory Notes: The status of the territory can also be described as "undetermined," or as an "independent customs area."

The Significance of the Specification of a "Receiving Country" for a Territorial Cession in a Peace Treaty

The designation of a "receiving country" for a territorial cession in a peace treaty means that the Legislative Branch of the "receiving country" is authorized to pass legislation to establish civil government in the territory.

Explanatory Notes: (A) It should be recognized that at the point of cession, the territory is actually being ceded to the military government of the principal occupying power. (B) Before the receiving country's civil government begins operations, the territory remains under the jurisdiction of the principal occupying power and in "interim status." (C) Without the appropriate specifications in a treaty, there is no authorization for any "country" to establish civil government in the territory, and military government (of the principal occupying power) continues until legally supplanted.

Occupied territory is "foreign territory"

See Downes v. Bidwell, 182 U.S. 244 (1901)
So long as Congress has not incorporated the territory into the United States, neither military occupation nor cession by treaty makes the conquered territory domestic territory, in the sense of the revenue laws; but those laws concerning "foreign countries" remain applicable to the conquered territory until changed by Congress. Such was the unanimous opinion of this court, as declared by Chief Justice Taney in Fleming v. Page, (1850) 9 How. 603, 617, 13 L. ed. 276, 281.

See Birkhimer, p. 1
From a belligerent point of view, therefore, the theatre of military government is necessarily foreign territory.
See Birkhimer, p. 21
Military government foreign territory
The erection of such governments over the persons and territory of a public enemy is an act of war; is in fact the exercise of hostilities without the use of unnecessary force. It derives its authority from the customs of war, and not the municipal law.
See Birkhimer, p. 43
Important consequences, occupied territory regarded as foreign
Important consequences result from the rule that territory under military government is considered foreign.

Hence, the statement that

Taiwan an occupied territory of the United States.
is indeed equivalent to saying that

Taiwan is under the jurisdiction of the United States Military Government (USMG).
but is not equivalent to saying that

Taiwan is part of the United States.

The Fiduciary Relationship between the Principal Occupying Power, the Occupied Territory, and the Local Inhabitants

See Fiduciary Relationships

Civil (Affairs) Administration of Military Government is still Military Government

See Birkhimer, p. 44
The position of the United States military authorities in Cuba, before the Spanish authorities abandoned the island in 1899, was one of military occupation, pure and simple; after that event, it was military occupation of a particular kind -- namely, wherein the dominant military power exercised authority over the island as trustee for a Cuban nation not yet in existence, but the creation of which was promised and which was to have the assistance of the United States in establishing itself.

During the former period the dominant military power exercised the authority of a conqueror in all his plenitude. During the latter period the United States military authorities governed, indeed, wholly by the rights of war, yet at no time did they lose sight of the fact that they were acting in the interests of the future Cuban nation. The government might be styled civil, but it was military for every necessary purpose . . . . .

See FM 27-10

368. Nature of Government
It is immaterial whether the government over an enemy's territory consists in a military or civil or mixed administration. Its character is the same and the source of its authority the same. It is a government imposed by force, and the legality of its acts is determined by the law of war.

(IV) USMG jurisdiction over SFPT Article 3 and Article 2b cessions

San Francisco Peace Treaty (April 28, 1952), relevant articles

Article 2
(b) Japan renounces all right, title and claim to Formosa and the Pescadores.

Article 3
Japan will concur in any proposal of the United States to the United Nations to place under its trusteeship system, with the United States as the sole administering authority, Nansei Shoto south of 29deg. north latitude (including the Ryukyu Islands and the Daito Islands), Nanpo Shoto south of Sofu Gan (including the Bonin Islands, Rosario Island and the Volcano Islands) and Parece Vela and Marcus Island. Pending the making of such a proposal and affirmative action thereon, the United States will have the right to exercise all and any powers of administration, legislation and jurisdiction over the territory and inhabitants of these islands, including their territorial waters.

Article 4
(b) Japan recognizes the validity of dispositions of property of Japan and Japanese nationals made by or pursuant to directives of the United States Military Government in any of the areas referred to in Articles 2 and 3.

Important definition

Property --
(1) something, as land and assets, legally possessed,
(2) a piece of real estate,
(3) something tangible or intangible to which its owner has legal title,
(4) the right of ownership; title.

Explanatory Notes: In regard to the disposition of the Ryukyus, the Office of US High Commissioner on Okinawa (Ryukyus) ceased on May 15, 1972 when the sovereignty of the island chain was transferred to Japan. In other words, USMG jurisdiction over this Article 3 territory was supplanted by a Japanese civil government. This date of May 15, 1972 was fully announced and widely publicized, and indeed has become part of the historical and legal record.

Contrastingly, no announcement of the end of USMG jurisdiction over the Article 2b cession of "Formosa and the Pescadores" has been forthcoming.

(V) Relevant Supreme Court Decisions

"The right to thus occupy an enemy's country and temporarily provide for its government has been recognized by previous action of the executive authority, and sanctioned by frequent decisions of this court. The local government being destroyed, the conqueror may set up its own authority, and make rules and regulations for the conduct of temporary government, and to that end may collect taxes and duties to support the military authority and carry on operations incident to the occupation."
Macleod v. U.S, 229 U.S. 416 (1913)

"The right of one belligerent to occupy and govern the territory of the enemy while in its military possession is one of the incidents of war, and flows directly from the right to conquer. We therefore do not look to the Constitution or political institutions of the conqueror for authority to establish a government for the territory of the enemy in his possession, during its [182 U.S. 222, 231] military occupation, nor for the rules by which the powers of such government are regulated and limited. Such authority and such rules are derived directly from the laws of war, as established by the usage of the world and confirmed by the writings of publicists and decisions of courts,- in fine, from the law of nations. . . . The municipal laws of a conquered territory or the laws which regulate private rights, continue in force during military occupation, except so far as they are suspended or changed by the acts of the conqueror. . . . He, nevertheless, has all the powers of a de facto government, and can at his pleasure either change the existing laws or make new ones."
Dooley v. U.S., 182 U.S. 222 (1901)

"Look at it practically from another point of view. Certainly, before revenue laws can be made operative in a district or country it is essential that the situation be taken into account, for the purpose of establishing ports of entry, collection districts, and the necessary [182 U. S. 222, 242] machinery to enforce them. Of course, it is patent that such investigations cannot be made prior to acquisition. But, as the laws immediately extend, without action of Congress, as the result of acquisition, it must follows that they extend, although none of the means and instrumentalities for their successful enforcement can possibly be devised until the acquisition is completed. This must be, unless it be held that there is power in the government of the United States to enter a foreign country, examine its situation, and enact legislation for it before it has passed under the sovereignty of the United States. From the point of view of the United States, then, it seems to me that the doctrine of the immediate placing of the tariff laws outside the line of newly acquired territory, however extreme may be the opinion entertained of the doctrine of immediate incorporation, is inadmissible and in conflict with the Constitution."
Dooley v. U.S., 182 U.S. 222 (1901)

"The jurisdiction of the conqueror is complete. He may change the form of government and the laws at his pleasure, and may exercise every attribute of sovereignty. The conquered territory becomes a part of the domain of the conqueror, subject to the right of the nation to which it belonged to recapture it if they can. By reason of this right to recapture, the title of the conqueror is not perfect until confirmed by treaty of peace. But this imperfection in his title is, practically speaking, important only in case of alienation made by the conqueror before treaty. If he sells, he sells subject to the right of recapture."

"But although, for purposes of sale, the title of the conqueror is imperfect before cession, for purposes of government and jurisdiction his title is perfect before cession. As long as he retains possession he is sovereign; and not the less sovereign because his sovereignty may not endure for ever. [50 U.S. 603, 608] Grotius (ch. 6, book 3, 4), speaking of the right to things taken in war, says that land is reputed lost which is so secured by fortifications that without their being forced it cannot be repossessed by the first owner. And in ch. 8, book 3, treating of empire over the conquered, he shows that sovereignty may be acquired by conquest."
Fleming v. Page, 50 U.S. 603 1850

"1st. That, by conquest and firm military occupation of a portion of an enemy's country, the sovereignty of the nation to which the conquered territory belongs is subverted, and the sovereignty of the conqueror is substituted in its place."

"2d. That although this sovereignty, until cession by treaty, is subject to be ousted by the enemy, and therefore does not give an indefeasible title for purposes of alienation, yet while it exists it is supreme, and confers jurisdiction without limit over the conquered territory, and the right to allegiance in return for protection."
Fleming v. Page, 50 U.S. 603 (1850)

"It cannot be denied that these principles, established by the common consent of the civilized world, must govern the title to conquests made by the United States. As one of the family of nations, they are bound by the law of nations, and the nature and effect of their acquisitions by conquest must be defined and regulated by that law."
Fleming v. Page, 50 U.S. 603 (1850)

"The messages of the President to Congress during the war, and the instructions from the heads of departments, contain authoritative declarations as to the right of the United States to acquire foreign territory by conquest, and as to the effect of such conquest upon the sovereignty of the conquered territory, in accordance with the principles above stated. Thus, the President, in his message of December, 1846, says:- 'By the law of nations a conquered territory is subject to be governed by the conqueror during his military possession, and until there is either a treaty of peace or he shall voluntarily withdraw from it. The old civil government being necessarily superseded, it is the right and duty of the conqueror to secure his conquest, and to provide for the maintenance of civil order and the rights of the inhabitants. This right has been exercised and this duty performed by our military and naval commanders, by the establishment of temporary governments in some of the conquered provinces in Mexico, assimilating them as far as practicable to the free institutions of our own country."
Fleming v. Page, 50 U.S. 603 (1850)

"A war, therefore, declared by Congress, can never be presumed to be waged for the purpose of conquest or the acquisition of territory; nor does the law declaring the war imply an authority to the President to enlarge the limits of the United States by subjugating the enemy's country. The United States, it is true, may extend its boundaries by conquest or treaty, and [50 U.S. 603, 615] may demand the cession of territory as the condition of peace, in order to indemnify its citizens for the injuries they have suffered, or to reimburse the government for the expenses of the war. But this can be done only by the treaty-making power or the legislative authority, and is not a part of the power conferred upon the President by the declaration of war. His duty and his power are purely military. As commander-in-chief, he is authorized to direct the movements of the naval and military forces placed by law at his command, and to employ them in the manner he may deem most effectual to harass and conquer and subdue the enemy. He may invade the hostile country, and subject it to the sovereignty and authority of the United States. But his conquests do not enlarge the boundaries of this Union, nor extend the operation of our institutions and laws beyond the limits before assigned to them by the legislative power."
Fleming v. Page, 50 U.S. 603 (1850)

"The theory that a country remains foreign with respect to the tariff laws until Congress has acted by embracing it within the customs union presupposes that a country may be domestic for one purpose and foreign for another. It may undoubtedly become necessary for the adequate administration of a domestic territory to pass a special act providing the proper machinery and officers, as the President would have no authority, except under the war power, to administer it himself; but no act is necessary to make it domestic territory if once it has been ceded to the United States. . . . This theory also presupposes that territory may be held indefinitely by the United States; that it may be treated in every particular, except for tariff purposes, as domestic territory; that laws may be enacted and enforced by officers of the United States sent there for that purpose; that insurrections [183 U.S. 176, 179] may be suppressed, wars carried on, revenues collected, taxes imposed; in short, that everything may be done which a government can do within its own boundaries, and yet that the territory may still remain a foreign country. That this state of things may continue for years, for a century even, but that, until Congress enacts otherwise, it still remains a foreign country. To hold that this can be done as matter of law we deem to be pure judicial legislation. We find no warrant for it in the Constitution or in the powers conferred upon this court. It is true the non action of Congress may occasion a temporary inconvenience; but it does not follow that courts of justice are authorized to remedy it by inverting the ordinary meaning of words."
The Diamond Rings, 183 U.S. 176 (1901)

We have no doubt, however, that, from the necessities of the case, the right to administer the government of Porto Rico continued in the military commander after the ratification of the treaty and until further action by Congress. Reference: Cross v. Harrison, 16 How. 182, 14 L. ed. 896. At the same time, while the right to administer the government continued, the conclusion of the treaty of peace and the cession of the island to the United States were not without their significance.
Dooley v. U.S., 182 U.S. 222 (1901)

The next case is that of Cross v. Harrison, 16 How. 164, 14 L. ed. 889. This was an action of assumpsit to recover back moneys paid to Harrison while acting as collector at the port of San Francisco, for tonnage and duties upon merchandise imported from foreign countries into California between February 2, 1848,-- the date of the treaty of peace between the United States and Mexico,-- and November 13, 1849, when the collector appointed by the President (according to an act of Congress passed March 3, 1849) entered upon his duties. Plaintiffs insisted that, until such collector had been appointed, California was and continued to be after the date of the treaty a foreign territory, and hence that no duties were payable as upon an importation into the United States. The plaintiffs proceeded upon the theory, stated in the dictum in Fleming v. Page, that duties had never been held to accrue to the United States in her newly acquired territories until provision was made by act of Congress for their collection, and that the revenue laws had always been held to speak only as to the United States and its territories existing at the time when the several acts were passed. The collector had [182 U.S. 1, 185] been appointed by the military governor of California, and duties were assessed, after the treaty, according to the United States tariff act of 1846. In holding that these duties were properly assessed, Mr. Justice Wayne cited with apparent approval a dispatch written by Mr. Buchanan, then Secretary of State, and a circular letter issued by the Secretary of the Treasury, Mr. Robert J. Walker, holding that from the necessities of the case the military government established in California did not cease to exist with the treaty of peace, but continued as a government de facto until Congress should provide a territorial government. "The great law of necessity," says Mr. Buchanan, "justifies this conclusion. The consent of the people is irresistibly inferred from the fact that no civilized community could possibly desire to abrogate an existing government, when the alternative presented would be to place themselves in a state of anarchy, beyond the protection of all laws, and reduce them to the unhappy necessity of submitting to the dominion of the strongest."
De Lima v. Bidwell, 182 U.S. 1 (1901)

In order further to illustrate the view which was taken by the Executive branch of the government, of the existing condition of things in California, it is proper to insert an extract from a dispatch written by Mr. Buchanan, Secretary of State, to Mr. Voorhees, on the 7th of October, 1848. It is as follows:

"The President, in his annual message, at the commencement of the next session, will recommend all these great measures to Congress in the strongest terms, and will use every effort, consistent with his duty, to insure their accomplishment."

"In the mean time, the condition of the people of California is anomalous, and will require, on their part, the exercise of great prudence and discretion. By the conclusion of the Treaty of Peace, the military government which was established over them under the laws of war, as recognized by the practice of all civilized nations, has ceased to derive its authority from this source of power. But is there, for this reason, no government in California? Are life, liberty, and property under the protection of no existing authorities? This would be a singular phenomenon in the face of the world, and especially among American citizens, distinguished as they are above all other people for their law-abiding character. Fortunately, they are not reduced to this sad condition. The termination of the war left an existing government, a government de facto, in full operation, and this will continue, with the presumed consent of the people, until Congress shall provide for them a territorial government. The great law of necessity justifies this conclusion. The consent of the people is irresistibly inferred from the fact that no civilized community could possibly desire to abrogate an existing government, when the alternative presented would be to place themselves in a state of anarchy, beyond the protection of all laws, and reduce them to the unhappy necessity of submitting to the dominion of the strongest."

"This government de facto will, of course, exercise no power inconsistent with the provisions of the Constitution of the United States, which is the supreme law of the land."
Cross v. Harrison, 57 U.S. 164 (1853)

The territory had been ceded as a conquest, and was to be preserved and governed as such until the sovereignty to which it had passed had legislated for it. That sovereignty was the United States, under the Constitution, by which power had been given to Congress to dispose of and make all needful rules and regulations respecting the territory or other property belonging to the United States, ... with only such limitations as are expressed in the section in which this power is given. The government, of which Colonel Mason was the executive, had its origin in the lawful exercise of a belligerent right over a conquered territory. It had been instituted during the war by the command of the President of the United States. It was the government when the territory was ceded as a conquest, and it did not cease, as a matter of course, or as a necessary consequence of the restoration of peace. The President might have dissolved it by withdrawing the army and navy officers who administered it, but he did not do so. Congress could have put an end to it, but that was not done. The right inference from the inaction of both is, that it was meant to be continued until it had been legislatively changed. No presumption of a contrary intention can be made. Whatever may have been the causes of delay, it must be presumed that the delay was consistent with the true policy of the government.
Cross v. Harrison, 57 U.S. 164 (1853)

By the ratifications of the treaty of peace, Porto Rico ceased to be subject to the Crown of Spain, and became subject to the legislative power of Congress. But the civil government of the United States cannot extend immediately and of its own force over conquered and ceded territory. Theoretically, Congress might prepare and enact a scheme of civil government to take effect immediately upon the cession, but, practically, there always have been delays and always will be. Time is required for a study of the situation, and for the maturing and enacting of an adequate scheme of civil government. In the meantime, pending the action of Congress, there is no civil power under our system of government, not even that of the President as civil executive, which can take the place of the government which has ceased to exist by the cession. Is it possible that, under such circumstances, there must be an interregnum? We think clearly not. The authority to govern such ceded territory is found in the laws applicable to conquest and cession. That authority is the military power, under the control of the President as Commander in Chief. In the case of Cross v. Harrison, 16 How. 164, 14 L. ed. 889, a situation of this kind was referred to in the opinion of the court, where it said; "It [the military authority] was the government when the territory was ceded as a conquest, and it did not cease as a matter of course, or as a necessary consequence of the restoration of peace. The President might have dissolved it by withdrawing the army and navy officers who administered it, but he did not do so. Congress could have put an end to it, but that was not done. The right inference from the inaction of both is that it was meant to be continued until it had been legislatively changed. [214 U.S. 260, 266] No presumption of a contrary intention can be made. Whatever may have been the causes of delay, it must be presumed that the delay was consistent with the true policy of the government." Pp. 193, 194. And see Leitensdorfer v. Webb, 20 How. 176, 15 L. ed. 891, and opinion of Mr. Justice Gray in Downes v. Bidwell, 182 U.S. 244, 345 , 45 S. L. ed. 1088, 1128, 21 Sup. Ct. Rep. 770.

The authority of a military government during the period between the cession and the action of Congress, like the authority of the same government before the cession, is of large, though it may not be of unlimited, extent. In fact, certain limits, not material here, were put upon it in Dooley v. United States, 182 U.S. 222 , 45 L. ed. 1074, 21 Sup. Ct. Rep. 762, and Lincoln v. United States, 197 U.S. 419 , 49 L. ed. 816, 25 Sup. Ct. Rep. 455, though it was said in the Dooley Case, page 234: "We have no doubt, however, that, from the necessities of the case, the right to administer the government of Porto Rico continued in the military commander after the ratification of the treaty, and until further action by Congress," -- citing Cross v. Harrison, supra.
Santaigo v. Nogueras, 214 U.S. 260 (1909)

"Footnotes: Resolved by the Senate and House of Representatives of the United States of America in Congress assembled, That by the ratification of the treaty of peace with Spain it is not intended to incorporate the inhabitants of the Philippine islands into citizenship of the United States, nor is it intended to permanently annex said islands as an integral part of the territory of the United States; but it is the intention of the United States to establish on said islands a government suitable to the wants and conditions of the inhabitants of said island to prepare them for local self-government, and in due time to make such disposition of said islands as will best promote the interests of the United States and the inhabitants of said islands."
Cong. Rec., 55th Cong. 3d Sess. vol. 32, p. 1847.
The Diamond Rings, 183 U.S. 176 (1901)