Arsenal of Democracy
At the time , Germany and the Soviet Union had signed a non-aggression treaty under the Molotov–Ribbentrop Pact , and had jointly affected the Invasion of Poland ( 1939 ) , a "Realpolitik" deal that remained effective until Operation Barbarossa , the Nazi invasion of the Soviet Union , in 1941 . 
<triplet> Molotov–Ribbentrop Pact <subj> Soviet Union <obj> participant <triplet> Operation Barbarossa <subj> Soviet Union <obj> participant