The territory of Missouri is a portion of Louisiana, which was purchased of France, and belongs to the United States in full dominion; in the language of the Constitution, Missouri is their territory or property, and is subject like other territories of the United States, to the regulations and temporary government, which has been, or shall be prescribed by Congress. The clause of the Constitution which grants this power to Congress, is so comprehensive and unambiguous, and its purpose so manifest, that commentary will not render the power, or the object of its establishment, more explicit or plain.
The Constitution further provides that "new States may be admitted by Congress into this Union." As this power is conferred without limitation, the time, terms, and circumstances of the admission of new States, are referred to the discretion of Congress; which may admit new States, but are not obliged to do so--of right no new State can demand admission into the Union, unless such demand be founded upon some previous engagement of the United States.
When admitted by Congress into the Union, whether by compact or otherwise, the new State becomes entitled to the enjoyment of the same rights, and bound to perform the like duties as the other States; and its citizens will be entitled to all privileges and immunities of citizens in the several States.
The citizens of each State possess rights, and owe duties that are peculiar to, and arise out of the Constitution and laws of the several States. These rights and duties differ from each other in the different States, and among these differences none is so remarkable or important as that which proceeds from the Constitution and laws of the several States respecting slavery; the same being permitted in some States and forbidden in others.
The question respecting slavery in the old thirteen States had been decided and settled before the adoption of the Constitution, which grants no power to Congress to interfere with, or to change what had been so previously settled. The slave States, therefore, are free to continue or to abolish slavery. Since the year 1808 Congress have possessed power to prohibit and have prohibited the further migration or importation of slaves into any of the old thirteen States, and at all times, under the Constitution, have had power to prohibit such migration or importation into any of the new States or territories of the United States. The Constitution contains no express provision respecting slavery in a new State that may be admitted into the Union; every regulation upon this subject belongs to the power whose consent is necessary to the formation and admission of new States into the Union. Congress may, therefore, make it a condition of the admission of a new State, that slavery shall be forever prohibited within the same. We may, with the more confidence, pronounce this to be the true construction of the Constitution, as it has been so amply confirmed by the past decisions of Congress.