I'd have to call you on a, b, and d - Russia saw it as integral to their existence as a nation, and it had to happen pretty much exactly when it happened or they would lose their (very very small) chance ever again. As it stands Russia probably won't exist in 50 years thanks to the damage that Putin accelerated. Look into the geopolitics of it.

I recommend watching reports from RealLifeLore, Whatifalthist, CaspianReport and Peter Zeihan.