Crimea and Kuban were removed from Ukraine after soviet occupation, then "gifted" back in exchange for other territories of Ukraine of same size. However, Ukrainians, Tatars, and Greeks were exterminated first, to free space for Russian colonists.
You are making same mistake as many others. Russian Federation != Russia. If something was owned by Russia, then it doesn't mean that it should be owned by Russian Federation automatically.
Russian Federation tries to pretend like they are the only right owners of everything, viewing others nations as traitors, who need to be executed for their act of stealing from Mother Russia.
In reality, Russian Empire (AKA Jail of Nations) was disbanded. Each nation had right to create their own country. Actual Russia renamed itself into Ukraine. Russian Federation has same rights on territory of Russian Empire as other nations, but RF uses lies and fakes to pretend like it has more rights than others, then start wars and captures or tries to capture territories, which they newer owned in first place.
The Crimea didn't vote anything. Crimea was invaded by Russian army. "Referendum" was military action, with intention to distract people. I.e. it was just show, yet another Russian fake, not a real thing.
USA is major enemy for Russian Federation for decades. Many fighters in Donetsk region came from RF and believed that they are on war with USA. Many examples of their direct speech is available on YouTube.
I personally know some contributors to FOSS, which are helping Russian FSB in their war against USA, by consulting them or by implementing tech to help find dissidents and American spies. For example, Michael Shigorin: https://www.opennet.ru/~Michael%20Shigorin
