NATO also has nothing to do with it, even though Putin has made this claim directly.  He will not leave or return land if US leaves NATO or even if NATO was dissolved entirely, even before the revolution.  He also wrote about the ideology he holds that Ukraine is not a country.  He simply sees Ukraine as an ex-girlfriend and is angry that she left (common language from the natives).  Nothing else.  Ukraine is valuable territory and he is lamenting over history and how it used to be Russian.  That is the only factor that actually brought the war.