Russia has been refighting the Cold War since the day we got involved in Kosovo. In their mind it would be like Russia sending troops to Mexico to get involved in one of the many cartel wars there. Can you imagine the appearance of Russian gunships laying waste to a quarter of Mexico City? Americans would probably be OK with that, right?
Russia was pissed and has remained pissed since that took place. We enjoyed immensely good relations with the Russians before that (lived in Russia, treated very well.) Keep that in mind when that idiot Hillary Clinton showed up with her "reset" button. It was the wrong person (her husband was the one who went to war in Kosovo), with the wrong message, at the wrong time. They didn't even bother to get the Russian right on the button label. "Hey we really care about you and want better relations, but not enough give a damn about getting the one damn Russian word "reset" right." Can anyone here give me a good reason why we got so involved in Kosovo?
Furthermore, moving to Georgia. That actually was "all about oil!" and securing the natural gas lines located in South Ossetia and Abkhaza. Russia now occupies them and UN inspectors are not allowed in. Should we have went to War here? No. These places are crap holes and their people cut deals with the Russians. There is exactly no American interest in these areas of Georgia. Also, we were pretty tied up in our financial collapse right then and there was little will for stopping Putin over those geographical nothingburgers.
Syria was a big deal not because Syria itself, but because of the way we played it. You set red lines, you enforce red lines. That is the way the game is played. It was then Putin established who we were. He has absolutely no concern of what the United States can do to him. None. As far as Europe goes, he knows he can just shut off the gas and let them live off their solar and wind power for a couple of months until they shut up. Ironically France is immune from this because they are heavily leveraged with nuclear power. But they are still France.
I suspect that Putin does not want to annex Crimea because then he wouldn't hold his slim voting majority he uses to get puppets elected in Ukraine. He will demand permanent ownership of their base there, demand that his puppet be restored to power, and likely demand more easements for his gas lines going into Europe (likely what the whole adventure was about.) He's going to keep pumping his sweet, sweet gas into Europe while they continue mucking around with energy solutions that don't work until he becomes rich enough to keep buying the United States piece by piece. Kind of like China.