Will Spain kill Catalonians in the same way as the US puppet regime in Ukraine bombards Donbass civilians

i would hope not

Probably, they've been persecuting the Basque for centuries. The Moors were driven out almost entirely by the Inquisition, it's why there were a lot of coloured people in the court of Louis XVI. Don't blame the Yanks for that one, Spain's problems are of her own making.