During wwii, ussr almost came to a collapse because of operation barbarossa, and the west has to contain the russian war effort. Britain & usa offered lend lease support to russia, but they could only be delivered in two ways: Iran is strategic!! (also iran is a big oil producer, can"t let it fall to. Reza khan; balance relations with britain, russia & germany; cooperative relations with germany during. Operation countenance britain & ussr invaded iran (1942 1945) Reza khan"s son forced to be a pro-ally government; tripartite treaty of alliance: britain, the soviet union, Iran withdrawal of all foreign troops within 6 month of the end of the war; transit rights; iran"s political independence. Throughout those three years, ussr established communist parties in azerbaijan and kurdistan; Ussr wanted to extend the border and create a buffer zone (like poland); This is totally against what was previously agreed to.