Stalin pursued a strategy of facilitating the formation of a Polish government independent of (and in opposition to) the exile government in London by empowering the Polish communists. Among Polish communist organizations established during the war were the Polish Workers' Party in occupied Poland and the Union of Polish Patriots in Moscow. A new was formed in the Soviet Union to fight together with the Soviets. At the same time Stalin worked on co-opting the Western Allies (the United States led by President Franklin D. Roosevelt and the United Kingdom led by Prime Minister Winston Churchill), who, in terms of practical implementations, conformed to Stalin's views on Poland's borders and future government. The fate of Poland had been determined in a series of negotiations that included the conferences in Tehran, Yalta, and Potsdam. In 1944, the Polish Government-in-Exile approved and the underground in Poland undertook unilateral political and military actions aimed at establishing an independent Polish authority, but the efforts were thwarted by the Soviets. The Polish communists founded the State National Council in 1943/44 in occupied Warsaw and the Polish Committee of National Liberation in July 1944 in Lublin, after the arrival of the Soviet army. The Soviet Union kept the eastern half of prewar Poland, granting Poland instead the greater southern portion of the eliminated German East Prussia and shifting the country west to the Oder–Neisse line, at the expense of Germany.