Prior to the Yalta Conference, the three leaders met in November 1943 in Tehran, Iran, where they coordinated the next phase of war against the Axis Powers in Europe and the Pacific.

At the Tehran Conference, the United States and Britain had committed to launching an invasion of northern France in mid-1944, opening another front of the war against Nazi Germany. Stalin, meanwhile, had agreed in principle to join the war against Japan in the Pacific after Germany was defeated.

By February 1945, as Roosevelt, Churchill and Stalin gathered again at Yalta, an Allied victory in Europe was on the horizon. Having liberated France and Belgium from Nazi occupation, the Allies now threatened the German border; to the east, Soviet Union troops had driven back the Germans in Poland, Bulgaria and Romania and gotten within 40 miles of Berlin.

This put Stalin at a distinct advantage during the meeting at the Black Sea resort, a location he himself had proposed after insisting his doctors had barred him from traveling long distances.

While the war in Europe was winding down, Roosevelt knew the United States still faced a protracted struggle against Japan in the Pacific War, and wanted to confirm Soviet support in an effort to limit the length of and casualties sustained in that conflict. At Yalta, Stalin agreed that Soviet forces would join the Allies in the war against Japan within "two or three months" after Germany’s surrender.

In return for its support in the Pacific War, the other Allies agreed, the Soviet Union would gain control of Japanese territory it had lost in the Russo-Japanese War of 1904-05, including southern Sakhalin (Karafuto) and the Kuril Islands.

Stalin also demanded that the United States grant diplomatic recognition of Mongolia’s independence from China: the Mongolian People’s Republic, founded in 1924, was a Soviet satellite.

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At Yalta, the Big Three agreed that after Germany’s unconditional surrender, it would be divided into four post-war occupation zones, controlled by U.S., British, French and Soviet military forces. The city of Berlin would also be divided into similar occupation zones.

France’s leader, Charles de Gaulle, was not invited to the Yalta Conference, and Stalin agreed to include France in the post-war governing of Germany only if France’s zone of occupation was taken from the US and British zones.

The Allied leaders also determined that Germany should be completely demilitarized and “denazified,” and that it would assume some responsibility for post-war reparations, but not sole responsibility.

Stalin took a hard line on the question of Poland, pointing out that within three decades, Germany had twice used the nation as a corridor through which to invade Russia. He declared that the Soviet Union would not return the territory in Poland that it had annexed in 1939, and would not meet the demands of the Polish government-in-exile based in London.

Stalin did agree to allow representatives from other Polish political parties into the communist-dominated provisional government installed in Poland, and to sanction free elections there—one of Churchill’s key objectives.

In addition, the Soviets promised to allow free elections in all territories in Eastern Europe liberated from Nazi occupation, including Czechoslovakia, Hungary, Romania and Bulgaria.

In return, the United States and Britain agreed that future governments in Eastern European nations bordering Soviet Union should be “friendly” to the Soviet regime, satisfying Stalin’s desire for a zone of influence to provide a buffer against future conflicts in Europe.

At Yalta, Stalin agreed to Soviet participation in the United Nations, the international peacekeeping organization that Roosevelt and Churchill had agreed to form in 1941 as part of the Atlantic Charter. He gave this commitment after all three leaders had agreed on a plan whereby all permanent members of the organization’s Security Council would hold veto power.

Having discussed these key issues, the Big Three agreed to meet again after Germany’s surrender, in order to finalize the borders of post-war Europe and other outstanding questions.

“There is no doubt that the tide of Anglo-Soviet-American friendship had reached a new high,” wrote James Byrnes, who accompanied Roosevelt to Yalta, in his memoirs. Though Roosevelt and Churchill also considered the Yalta Conference an indication that their wartime cooperation with the Soviets would continue in peacetime, such optimism would prove to be short-lived.

By March 1945, it had become clear that Stalin had no intention of keeping his promises regarding political freedom in Poland. Instead, Soviet troops helped squash any opposition to the provisional government based in Lublin, Poland. When elections were finally held in 1947, they predictably solidified Poland as one of the first Soviet satellite states in Eastern Europe.

Many Americans criticized Roosevelt—who was seriously ill during the Yalta Conference and died just two months later—for the concessions he made at Yalta regarding Soviet influence in Eastern Europe and Northeast Asia.

President Harry Truman, Roosevelt’s successor, would be far more suspicious of Stalin that July, when the leaders of the Allied powers met again at the Potsdam Conference in Germany to hash out the final terms for ending World War II in Europe.

But with his troops occupying much of Germany and Eastern Europe, Stalin was able to effectively ratify the concessions he won at Yalta, pressing his advantage over Truman and Churchill (who was replaced mid-conference by Prime Minister Clement Attlee).

In March 1946, barely a year after the Yalta Conference, Churchill delivered his famous speech declaring that an “iron curtain” had fallen across Eastern Europe, signaling a definitive end to cooperation between the Soviet Union and its Western allies, and the beginning of the Cold War.

READ MORE: How the 'Big Three' Teed Up the Cold War at the 1945 Yalta Conference

The Yalta Conference 1945. Office of the Historian, U.S. Department of State.
Terry Charman, “How Churchill, Roosevelt and Stalin Planned to End the Second World War.” Imperial War Museums, January 12, 2018.
The End of World War II and the Division of Europe. Center for European Studies, The University of North Carolina at Chapel Hill.