California was an independent republic briefly before it joined the United States.
Crimea declared independence in 1992. It refers to itself as an autonomous republic, with its own constitution.
Ah yes! Now I remember. California, like Texas, became an independent (From Mexico) republic after English speaking immigrants from the US rebelled and declared independence, then petitioned the US for annexation.
The difference in the Ukraine, as I understand it, is that the Russian speaking Crimeans are not immigrants...but I could be wrong.
Then there is the Reconquista movement of Spanish speaking immigrants in the SW US...
“What difference, at this point, does it make?” HRC
“Borders, language, culture” MS