ujm, you seem to be reading from a Soviet textbook, maybe absorbed through some American academics. Ukraine actually was a country for a short period in about 1918. Before Russia, it was Poland and Austro-Hungary. Jews went there on their own having an opportunity to work the estates as representatives of Polish nobles. Crimea used to be Tatar, even after it became Russian. Soviets exiled them all (most died on the way) around WW2 somewhere. One reason Turkey is supporting Ukrainians.
A simple point is that country borders were internationally recognized after USSR dissolved on their own. If Russia can claim Crimea, then Germany can claim Danzig from Poland and Kaliningrad from Russia; Poland – Vilno from Lita; Sweden – Petersburg from Russia; and Mongols – the rest of Russia.
All of Europe seemingly learned to live in a modern world without fighting each other, Russia and Belorussia are the only holdouts.