At the Yalta Conference in February 1945, Stalin was able to present his western allies, Franklin Roosevelt and Winston Churchill, with a "fait accompli" in Poland. His armed forces were in occupation of the country, and his agents, the communists, were in control of its administration. The Soviet Union was in the process of incorporating the lands in eastern Poland, including the mass expulsion of the Polish population, which it had occupied between 1939 and 1941, after participating in the invasion and partition of Poland with Nazi Germany. Stalin was determined that Poland's new government would become his tool towards making Poland a Soviet puppet state controlled by the communists. He had severed relations with the Polish government-in-exile in London in 1943, but to appease Roosevelt and Churchill he agreed at Yalta that a coalition government would be formed. The Soviet Union supported Polish demands to be compensated by the loss of the former East of Poland, from which 2-3 millions Polish citizens were expelled, by German lands east of the rivers Oder and Lusatian Neisse which had homed 9 million Germans. Stalin allowed Polish authorities to