Putin has always been clear of his intent to retake the Ukraine, which is why NATO was never willing to offer it full NATO membership knowing it woujld trigger a war they wanted no part of. So why invade at this moment? Because Putin made the calculation that the last five years so deeply politically and socially divided the US that it would be unable to respond strongly to the invasion, and without the US leading the way the European countries would quietly fold.
Which turned out to a mis-calculation, as this war is the only thing that could bring the center and moderate right and left together into a united response as this point in time, and so the US is out front in uniting the NATO allies to man up beginning with sanctions that will now swiftly escalate.
As it is, both the rubel as well as the Russian stock market are cratering today, next will be it's plutocrats fortunes and citizens standard of livintg as the west is cut off from trade, the bodies of Rusisian soldiers will start coming home, and then the true danger point will arrive.
Will Putin pull back, which his narcisstic pride will battle, or will he instead declare a war footing in the country and send his military over the Ukraine border into the neighboring countries that joined NATO after the collapse of the Russian empire, drawing NATO and the US into a ground war that could quickly escalate into battlefield nukes.
Let's sincerely hope that Putin suddenly comes down with a case of the 'Russian Flu' as the billionaires in the country realize they wil lose everything they've stolen from it's people if they let Putin continue on.