Political map of South & Southwest Asia 29 August 1941 (Anglo-Soviet invasion of Iran): When Germany invaded the Soviet Union in June 1941, Iran’s strategic position and oil reserves became even more important to the Allied war effort than before. In August the British and the Soviets launched a joint invasion of the country (Anglo-Soviet invasion of Iran), deposing the defiant Reza Shah and opening up a supply route to the Soviet Union (Persian Corridor).