It is interesting that Putin conscripted non-slavic or mixed slavic Russians at a much higher rate than white citizens of Moscow and St. Petersburg early on in the war.
The man referred to as "Putin's brain" is a Neo-Nazi named Aleksandr Dugin.
https://en.wikipedia.org/wiki/Aleksandr_Dugin
However, the main driver of this invasion was money, with the belief that Ukraine could not defend itself and that the West would largely ignore it, just like they did in 2014.