Communism

The Molotov-Ribbentrop pact was not societ "collaboration" with the Nazis. It was a self-preserving, non-aggression treaty between a rising fascist empire hell-bent on destroying workers movements like communism as all fascists are and a young workers movement that had been besieged since it's inception. It gave them the time they needed to industrialize and prepare for the inevitable war with the Germans which they sacrificed so much for. 80% of Nazis were killed by the red army and 27 million soviets died for it.

Calling that pact collaboration is incredibly direspectful to their history