US territories are a rather different situation because they are not sovereign entities in the way that US states are. US territories are essentially land owned and administered by the federal government so the federal government is free to acquire and dispose of them as it wishes. But the states are sovereigns in their own right that have entered into a compact vis-a-vis the federal government and the other states. Because the sovereignty of the federal government emerges from this compact of the collection of individual states, the federal government generally does not have the authority to modify the terms of the compact without the assent of the states.