"By the laws and usages of nations, conquest is a valid title.... As regarded by all other nations it [Tampico] was a part of the United States, and belonged to them as exclusively as a Territory included in our established boundaries, but yet it was not a part of the Union." (United States Supreme Court, Fleming et al. v. Page, 9 How. 603-615.)
A title so acquired by the United States cannot be questioned in its courts.
"If those departments which are intrusted with the foreign intercourse of the Nation ... have unequivocally asserted its rights of dominion over a country of which it is in possession and which it claims under a treaty, if the legislature has acted on the construction thus asserted, it is not in its own courts that this construction is to be denied. A question like this, respecting the boundaries of a nation, is ... more a political than a legal question, and in its discussion the courts of every country must respect the pronounced will of the legislature." (Mr. Chief Justice Marshall, Foster et al. v. Neilson, 2 Peters 253, 309.)
Yet such territory may be still outside the United States (meaning thereby the American Union organized by the Constitution—the Nation), and cannot get in without action by the political authorities.
"The boundaries of the United States, as they existed when war was declared against Mexico, were not extended by the conquest.... They remained unchanged. And every place which was out of the limits of the United States, as previously established by the political authorities of the Government, was still foreign." (Fleming et al. v. Page, 9 How. 616.)
The United States can govern such territory as it pleases. Thus it can withhold any power of local legislation.
"Possessing the power to erect a Territorial government for Alaska, they could confer upon it such powers, judicial and executive, as they deemed most suitable to the necessities of the inhabitants. It was unquestionably within the constitutional power of Congress to withhold from the inhabitants of Alaska the power to legislate and make laws. In the absence, then, of any law-making power in the Territory, to what source must the people look for the laws by which they are to be governed? This question can admit of but one answer. Congress is the only law-making power for Alaska." (United States v. Nelson, 29 Fed. Rep. 202, 205, 206.)
Mr. Jefferson even held that the United States could sell territory, hold it as a colony, or regulate its commerce as it pleased.
"The Territory [Louisiana] was purchased by the United States in their confederate capacity, and may be disposed of by them at their pleasure. It is in the nature of a colony whose commerce may be regulated without any reference to the Constitution." (And Louisiana was so governed for years after the purchase, with different tariff requirements from those of the United States, and without trial by jury in civil cases.)
Again, the United States may even (as in the case of Consular Courts) withhold the right of trial by jury.