The Collapse of the Grand Alliance

The problems started in Europe.

At the end of the war, Soviet military forces occupied all of Eastern Europe and the Balkans (except Greece, Albania, and Yugoslavia), while U.S. and other Allied forces secured the western part of the Continent. 

Roosevelt had assumed that free elections, administered promptly by “democratic and peace-loving forces,” would lead to democratic governments responsive to the local population.

But it soon became clear that the Soviet Union interpreted the Yalta agreement differently. 

When Soviet occupation authorities began forming a new Polish government, Stalin refused to accept the Polish government-in-exile—headquartered in London during the war and composed mostly of landed aristocrats who harbored a deep distrust of the Soviet Union—and instead set up a government composed of Communists who had spent the war in Moscow.

Roosevelt complained to Stalin but eventually agreed to a compromise whereby two members of the London government were included in the new Communist regime.

A week later, Roosevelt was dead of a cerebral hemorrhage, embolding Stalin to do much as he pleased.