This thesis concerns the occupation of Iran during World War II, in 1941 by the Soviet Union and Great Britain and its aftermath. The United States got involved in this through its lend-lease policy. When Iran refused to give oil concessions to the Soviets, a crisis developed between the two countries so much that at the end of the war the Soviets refused to leave the parts of Iran it occupied. Iran asked the US for support and referred the case to the nascent UN organisation. The thesis analyses US pressures on the Soviets both within and outside the UN. These led the Soviets to back down and leave Iran on May 6, 1946