Speaking from personal knowledge and family stories, Neo-Nazis took off after the fall of the Soviet Union. The Soviets had no toleration for it, and for example if you chose to walk around with a Nazi flag saying “Hell Hitler” anywhere in the Union, you would probably be beaten to death by everyone around you before the police even showed up.

Everyone lost someone in the war, not to mention the Holocaust.

A lot of groups were sponsored by American or Weatern European hate groups in order to prop up support and find new members. The internet was also a horrific catalyst for a lot of Nazi thought.

A lot of exiled degenerates who defected to the Nazis came back or were rehabilitated and started spewing their thought.