In compensation , the USSR gave Poland former German populated territories in Pomerania , Silesia , and Brandenburg east of the Oder – Neisse line , plus the southern half of East Prussia . These awards were confirmed at the Tripartite Conference of Berlin , otherwise known as the Potsdam Conference in August 1945 after the end of the war in Europe . 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 communists held a majority of key posts in this new government , and with Soviet support they soon gained almost total control of the country , rigging all elections
Potsdam Conference
Potsdam Conference
Polish People's Republic