The Law Regarding "Conquered Territory"
Under the Jus Gentium, a distinction is made between a "possession," a "dependency" and a "colony." A possession is a country that is held by another by no other title but mere conquest. A dependency is territory within the rightful dominion of a country. A colony is a country that is settled by citizens or subjects of the mother country.
A further distinction is made in governing a colonized "wasteland," (or vacant land,) and a land acquired by treaty or cession that had already been cultivated and organized. If an uninhabited country was discovered and planted by the mother country, the laws of the mother country were said to be immediately in force there.
A different rule applied to conquered and ceded countries that already had laws of their own. In such cases, the conqueror had a right to abrogate the former laws and institute new ones. Until such new laws were promulgated, the old laws and customs of the country remained in full force to the extent that they are not contrary to religion or morals.
The Jus Gentium was adhered to in the settlement of the western American frontiers:
According to the April, 1956, report (Part I), pages 156-161 of the Interdepartmental Committee "Study Of Jurisdiction Over Federal Areas Within The States," this principle was explained in the case of Chicago, Rock Island & Pacific Ry. v. McGlinn, 114 U.S. 542 (1885):
"It is a general rule of public law, recognized and acted upon by the United States, that whenever political jurisdiction and legislative power over any territory are transferred from one nation or sovereign to another, the municipal laws of the country, that is, laws which are intended for the protection of private rights, continue in force until abrogated or changed by the new sovereign. By the cession public property passes from one government to the other, but private property remains as before, and with it those municipal laws which are designed to secure its peaceful use and enjoyment. As a matter of course, all laws, ordinances, and regulations in conflict with the political character, institutions, and constitution of the new government are at once displaced.
"Thus, upon a cession of political jurisdiction and legislative power--and the latter is involved in the former- to the United States, the laws of the country in support of an established religion, or abridging the freedom of the press, or authorizing cruel and unusual punishments, and the like, would at once cease to be of obligatory force without any declaration to that effect; and the laws of the country on other subjects would necessarily be superseded by existing laws of the new government upon the same matters. But with respect to other laws affecting the possession, use and transfer of property, and designed to secure good order and peace in the community, and promote its health and prosperity, which are strictly of a municipal character, the rule is general, that a change of government leaves them in force until, by direct action by the new government, they are altered or repealed. American Insurance Co. v. Canter, 1 Pet. 542; Halleck, International Law, ch. 34, Sec. 14."] (Empasis mine.)
(Reference: John Bouvier, A Law Dictionary Adapted to the Constitution and Laws of the United States of America and the Several States of the American Union, Childs & Peterson, c1856.)
CONQUEST, international law. The acquisition of the sovereignty of a country by force of arms, exercised by an independent power which reduces the vanquished to the submission of its empire.
2. It is a general rule, that where conquered countries have laws of their own, these laws remain in force after the conquest, until they are abrogated, unless they are contrary to our religion, or enact any malum in se. In all such cases the laws of the conquering country prevail; for it is not to be presumed that laws opposed to religion or sound morals could be sanctioned. 1 Story, Const. Sec. 150, and the cases there cited.
4. Conquest does not, per se, give the conqueror plenum dominium et utile, but a temporary right of possession and government. 2 Gallis. R. 486; 3 Wash. C. C. R. 101. See 8 Wheat. R. 591; 2 Bay, R. 229; 2 Dall. R. 1; 12 Pet. 410.
5. The right which the English government claimed over the territory now composing the United States, was not founded on conquest, but discovery. Id. Sec. 152, et seq.