In September 1939 the Soviet Union under Joseph Stalin had annexed Eastern Poland in cooperation with Nazi Germany, displacing many Poles, and triggering the outbreak of the Second World War with the Allies, including the British Empire. Once Nazi Germany attacked the USSR in June 1941, the British Empire and USSR established friendly relations and efforts were made to improve conditions for displaced Poles. Between August 24, 1942 and December 31, 1944 Polish refugees were evacuated from the USSR via the "Persian Corridor" in Iran and over thirty thousand of them were housed in refugee camps and were settled in Karachi (then part of British India), which was the nearest major port. Some remained in Karachi, becoming citizens of the newly established State of Pakistan in 1947.