I think this is a purely rational decision on his part.

He senses weakness in the west, and particularly the US in an election year. He wants Ukraine. He’s not pleased about Khazakstan and our possible role there. He has a good relationship with China and they aren’t yet in a position to try to stop this.

And to Chris’ point, he’ll keep escalating until he wins. You don’t want a completely destroyed country, but he’ll destroy enough to win.