Everything was going swimmingly with Russia from 1991 right up until 1999, and then NATO bombed Belgrade. There was a huge amount of ignorance in the West about the effect this would have on the Russian brain and its tendency towards paranoia, especially about the objectives of NATO in general and America in particular.
Then there was GW2 and the basing of ABMs in former Warsaw Pact countries, and all the while the Russians were watching and becoming increasingly anxious - when would they be next? The Russians saw nations like Albania, the Czech Republic, and Romania join NATO and that was pretty much it, they were alone, isolated, and without alllies - a reaction was inevitable, they are scared, and that is a very, very dangerous thing.
There was a seminal moment just a few weeks ago and that was the Russian attack on At-Tanf in Syria, a joint US/UK base - at that point the game switched from sabre rattling to an open attempt to kill US and UK personnel.
I don't believe the Russians want open conflict, but I do believe they are more than happy to oblige us if it becomes necessary to assert dominance in Syria, and push us back in Europe.
Just my own uninformed analysis of the situation.