Was it also the fault of Cambodians that Pol Pot genocided them?

Pol Pot would never happen if there was no colonial ambitions and meddling of U.S. and France in the region.

The fault of the peoples of the USSR that Stalin genocided them?

That’s a common Western myth. Stalin never genocided anybody, which was evident by the great rise of USSR population during his reign DESPITE the terrible loses during WWII, and the late professor Stephen Cohen has documented it very well in his books.