How did the original colonies enter? And where is the prohibition against leaving? Just curious.
Jay, Chief Justice:-- The Question we are now to decide has been accurately stated, viz.: Is a state suable by individual citizens of another state?...
The revolution, or rather the Declaration of Independence, found the people already united for general purposes, and at the same time, providing for their more domestic concerns by state conventions, and other temporary arrangements. From the crown of Great Britain, the sovereignty of their country passed to the people of it; and it was then not an uncommon opinion, that the unappropriated lands, which belonged to that crown, passed, not to the people of the colony or states within whose limits they were situated, but to the whole people; on whatever principles this opinion rested, it did not give way to the other, and thirteen sovereignties were considered as emerged from the principles of the revolution, combined with local convenience and considerations; the people nevertheless continued to consider themselves, in a national point of view, as one people; and they continued without interruption to manage their national concerns accordingly; afterwards, in the hurry of the war, and in the warmth of mutual confidence, they made a confederation of the States, the basis of a general Government.
Experience disappointed the expectations they had formed from it; and then the people, in their collective and national capacity, established the present Constitution. It is remarkable that in establishing it, the people exercised their own rights and their own proper sovereignty, and conscious of the plenitude of it, they declared with becoming dignity, "We the people of the United States," 'do ordain and establish this Constitution." Here we see the people acting as the sovereigns of the whole country.; and in the language of sovereignty, establishing a Constitution by which it was their will, that the state governments should be bound, and to which the State Constitutions should be made to conform. Every State Constitution is a compact made by and between the citizens of a state to govern themeselves in a certain manner; and the Constitution of the United States is liekwise a compact made by the people of the United States to govern themselves as to general objects, in a certain manner. By this great compact however, many prerogatives were transferred to the national Government, such as those of making war and peace, contracting alliances, coining money, etc."
Wilson, Justice-- "Whoever considers, in a combined and comprehensive view, the general texture of the constitution, will be satisfied that the people of the United States intended to form themselves into a nation for national purposes. They instituted, for such purposes, a national government complete in all its parts, with powers legislative, executive and judiiciary, ad in all those powers extending over the whole nation."
-- From "Chisholm v. Georgia", 1793
The Supreme Court is amply on the record to answer your question.
The whole Constitution forbids secession.