 When the Soviet Red Army invaded and then occupied Eastern Poland in accordance with the Molotov–Ribbentrop Pact, Anielewicz heard that Jewish refugees, other youth movement members and political groups had flocked to Wilno, which was then under Soviet control.Anielewicz travelled to Wilno and attempted to convince his colleagues to send people back to other Polish occupied territories to continue the fight against the Germans.He then attempted to cross the Romanian border in order to open a route for young Jews to get to the Mandate of Palestine, but was caught and thrown into the Soviet jail.