The following link describes some US states that used to be independent countries: Vermont, Texas, California, Hawaii, Utah, and Oregon/Washington. https://ammo.com/articles/sovereign-states-america-history-independent-states-joined-us-union
The link leaves out the fact that the original 13 colonies were free and independent sovereign countries during the war for Independence, only delegating authority to a central government when they ratified the Constitution. It also doesn’t mention the State of Franklin (1784-1788 in Tennessee territory). We could also mention AmerIndian nations.
Most importantly, the US Constitution says that any state admitted to the Union has the same status and privileges as the original founding states. This means that every state in the Union has the same basis to secede from the Union as the original 13 colonies (states).