To say anyone else but Hitler is responsible is playing into the game that individuals aren’t responsible for anything but just reacting to forces beyond their control, so can’t be blamed. So basically Hitler has no free will, but Russia and/or the West are responsible
What?!? No, what people are saying is that: first, it would have been much riskier for Hitler to have invaded Poland without the pact with Russia, so the pact made war more likely. This is a fact, which has nothing to do with "free will"... just common sense. And secondly, as soon as Poland was crushed in the West by the Wehrmacht, the USSR took advantage of this to invade and conquer part of a sovereign nation. This is also an indisputable fact.
The Russian argument is a little bit like arguing that, after watching a passerby get mugged, beaten senseless, and robbed of his wallet, it's also OK for you to step in to steal the watch off of his arm as he lies there unconscious. Sorry, no one with any sense or morality would agree...