Most of the world has a complex history of interchanging dominion. I call it bygone History. However, in the 20th Century we reached a state of "homeostasis" with the creation of the United Nations and formalized International Laws so any attempts to revert to bygone borders is seen as barbaric conquest and unnecessary. Since Russia already has a surface area larger than Pluto, they have no compelling reason to own Crimea and could enjoy it as a peaceful neighbor but since they have fallen into the hands of a brutal dictator they must abide by his whims which he props up with bygone patriotic fervor using his grip on the media. Because Russia had made an Agreement to exchange Ukraine's nuclear arsenal for security assurances, its subsequent conquests are all the more egregious and immoral. By International Law and the forces of History, Crimea ended up belonging to Ukraine and anything else is fantasy and delusion.