During the Second World War, Lithuania, Latvia and Estonia were occupied on three separate occasions - twice by the Soviet Union and once by Nazi Germany. The signing of the Ribbentrop-Molotov Pact of 1939 allowed the Soviets to dominate the Baltic states without fear of German reprisals, causing many in the German-Baltic populations to flee to Poland.
Soviet rule of the Baltics was brutal with the purging of political elites and deportation of many tens of thousands in a bid to turn them into vassal states. Consequently, when Hitler launched Operation Barbarossa in June 1941, many Balts saw it as a liberation from Soviet cruelties.
The reality was, however, that it turned out to be the beginning of something much worse. During their occupation of Poland prior to Barbarossa the Nazis had decimated the Polish political elites, and the Jews there had been herded into ghettos in preparation for deportation to the east where they would serve as slave labour in the Nazi economy after the conquest of the Soviet Union. Similar policies were to be adopted in the Baltics when Reinhard Heydrich's murder squads, the Einsatzgruppen, were allowed to move into the newly-occupied territories.