I would argue it really isn't that complicated. When one is talking about an autocrat, it always comes down to maintenance of power + money. Much of these current events arguably was precipitated by the real support Navalny had inside of Russia to oppose Putin's regime, to the point where Putin tried to poison him in a foreign country and then now has put him in prison on sham accusations.
@Raoul has done a really good job of explaining these pro-democracy elements building in Russia. Now Putin sees a Ukraine that has had a couple of free elections and is working its way into the European community where many Russians would like to be, of course he sees that as a threat to his legitimacy. He now has the opportunity to "decommunise" and "denazify" this neighbor to restore his own legitimacy in his head.