Let's not dwell on historical facts, which are debated by scholars, who are we to participate?
The point is that Donbass is filled with ethnic Russians who settled there during the Soviet era, Crimea was 'gifted' to Ukraine during the Soviet era, perhaps there was no caveat attached to the gift, as nobody thought at the time that USSR would one day collapse and Ukraine would want to get a new husband in the form of EU/NATO. So if you at all know Russian mentality, then you would understand that Russia, Putin or be it another President, would never have allowed Crimea to be a part of a westernised Ukraine and in time to have NATO bases located there. It's a matter of principle for Russians. The Ukrainian language is different to the Russian language. Ukrainian traditions and folklore are also different from the Russian ones. There are many similarities of course. What has this to do with what's going on though?