This has been in the Russian plans for a long time.
Ukraine used to be part of the USSR and he wants it back for a lot of reasons. Had a russian girlfriend for about 2 years; learned a LOT more about them than I really needed to know.
The bigger problem is China. China and Russia are allies. If the USA were to retailiate against the Russians over Ukraine, China could very likely back the Russians. Now think on that a while. How'd China get as rich as they are?
Our former pres knew this and it was a good portion of what he was trying to accomplish. Cheap products drove manufacturing out of this country and into China which has created a massive power shift, not just militarily, but economically and productivity. Ukraine is a test for China. XI is waiting to see world reaction and response before making his move on Taiwan. Xi already made his move on Hong Kong, which is just a step away from full indoctrination into China, far earlier than the 50 years they were allowed.
To be honest, ever since the end of the cold war, we have become complacent. The threat of nukes flying around the world went away, only NK being a gnat in the world view, but now with Putin firing up the Nuke threats once again, we are heading into another cold war.
All those preppers are sitting back now saying, see, and you thought we were crazy.