Show me where the States agreed to give that up in the Constitution -- along with coining money, granting titles, and treating with foreign powers pro se.
Gotta be in Article I, Section 10 somewhere, right?
Point to the words, amigo.
Yes it is. The power to approve changes to the status of states is a power delegated to the United States, and the power to act unilaterally where the interests of other states are concerned are powers denied to the states.