[IAmBroom]

> They used to be called that because they were independent countries

The latter part is true of exactly one US state (Hawaii), but otherwise false. They are called that because they are political bodies capable of international relations. The 13 founding states were British colonies; Florida, New Mexico and Texas were famously Mexican and/or Spanish colonies, and the western half of the continental states were French colonies (though largely unexplored by France, so only nominally held).

[evanelias]

I believe GP is technically correct in several ways. The first 13 states were mostly independent and sovereign under the Articles of Confederation from 1781 until 1789, when the US Constitution superseded it and established a much more significant central government.

Texas was an independent republic from 1836 until US annexation at the end of 1845. Although Mexico did not recognize the independence of the Republic of Texas, numerous other countries did.

California is more of an edge-case. It was arguably an independent republic for a few weeks in 1846. And a similar story with Florida: the Republic of West Florida existed for a couple months in 1810. But both of these cases were basically small uprisings that weren't broadly recognized by other countries.