following germany's invasion of the ussr in june 1941, britain and the soviet union became allies. britain and the ussr saw the newly opened trans-iranian railway as an attractive route to transport supplies from the persian gulf to the soviet union. britain and the ussr used concessions extracted in previous interventions to pressure iran (and, in britain's case, iraq) into allowing the use of their territory for military and logistical purposes. increased tensions with britain led to pro-german rallies in tehran. in august 1941, because reza shah refused to expel all german nationals and come down clearly on the allied side, britain and the ussr invaded iran, arrested the monarch and sent him into exile to south africa, taking control of iran's communications and the coveted railway.