When Winston Churchill formed his wartime coalition government in 1940 he appointed Cripps Ambassador to the Soviet Union in the view that Cripps, who had Marxist sympathies, could negotiate with Joseph Stalin who had a nonaggression pact with Nazi Germany through the Molotov–Ribbentrop Pact. When Hitler attacked the Soviet Union in June 1941, Cripps became a key figure in forging an alliance between the western powers and the Soviet Union.