Near the end of World War II , the advancing Soviet Red Army , along with the Polish Army formed in the Soviet Union , pushed out the Nazi German forces from occupied Poland . In February 1945 , the Yalta Conference sanctioned the formation of a provisional government of Poland from a compromise coalition , until postwar elections . Joseph Stalin , the leader of the Soviet Union , manipulated the implementation of that ruling . A practically communist-controlled Provisional Government of National Unity was formed in Warsaw by ignoring the Polish government-in-exile based in London since 1940
Yalta Conference
Yalta Conference
History of Poland (1945–1989)