The Soviet Union moved quickly to almost entirely stamp out Judaism across the massive country within a decade of coming to power. By the 1930's virtually all major Jewish leaders in the world's largest Jewish community had either been killed, fled or went into hiding. 

One Jewish leader, Rabbi Levik Schneerson, the Rabbi of Dnipro in Ukraine survived and almost single handedly kept the Jewish spark alive. In 1939 he was arrested and sent to Kazakhstan where he died in 1944

A fascinating discussion about Rabbi Levik Schneerson and his role in standing up to the soviets.