Having suffered persecution by the Stalinist regime, many Mennonites came to identify with Adolf Hitler, who opposed Stalin, and subscribed to conspiracy theories blaming the Jews for Communist crimes. As pacifists within an increasingly military regime under Stalin and then (after invasion of Ukraine and parts of Russia by Hitler) the Nazis, and as "Volga Germans" whose abuse Hitler had used as pretense to invade, Mennonites were subject to special pressure to join military units. Mennonites played a central role in exploiting slave labor at Stutthof concentration camp, and some, recruited into SS units, served as guards at concentration camps or perpetrated massacres. Other Mennonites were conscripted by force into German units as support and shock troops and some participated in exterminating or deporting families. Most history of this period is anecdotal and based on family memoirs and letters from the Gulags.