While
German armies were highly successful against the
Soviet Union, the Iranian government expected Germany to win the war and establish a powerful force on its borders. It rejected British and Soviet demands to expel German residents from Iran. In response, the two
Allies invaded in August 1941 and easily overwhelmed the weak Iranian army in
Operation Countenance. Iran became the major conduit of Allied
Lend-Lease aid to the Soviet Union. The purpose was to secure Iranian
oil fields and ensure Allied
supply lines, through the
Persian Corridor. Iran remained officially neutral. Rezā Shāh was deposed during the subsequent occupation and replaced with his young son
Mohammad Reza Pahlavi.