The Yalta War Conference was held between February 4th and February 11th 1945. Yalta is on the Black Sea coast of the Crimea and a war meeting here in February 1945, was safe for those participating. The 'Big Three' were at this meeting: Joseph Stalin, Winston Churchill and F D Roosevelt.
What was achieved at Yalta?
Stalin agreed to enter the war against Japan.
Stalin agreed to collaborate with the establishment of the United Nations Organisation which had already been discussed at the Dumbarton Oaks meeting in 1944.
Churchill got Stalin to agree that France should have a zone of occupation in the defeated Germany
Stalin got an agreement that the Soviet/Polish border would be the Curzon Line and that the Polish/German border would be the Oder-Neisse Line.
Stalin agreed to free elections in Poland, to be held as quickly as was possible after the war had ended. Stalin agreed that members of the Polish government in exile could have a place in the new Polish government.
A “Declaration on Liberated Europe” was released which stated that all nations previously under German control would have a democratic government
Roosevelt received a far bit of criticism from political pundits in America once the points of Yalta were released. He was criticised for 'giving' Eastern Europe to Stalin. However, there was little else he could do. The simple military fact in February 1945 was that the Soviet Union dominated Eastern Europe and that the power of the atomic bomb (that had yet to be tested) was not known by the Americans who could not use it as a counter-measure to curb Stalin's ambitions.
Roosevelt was also criticised for allowing the Russians to get involved in the war against Japan. However, in February 1945, the Japanese still seemed a formidable opponent and American intelligence had estimated America could suffer 1 million casualties if she attempted to occupy Japan. There was the obvious 'card' to play - the Soviet Union had a vast army and it could easily make a huge impact in the war in the Far East, especially on the Asian mainland.