Although the United States and the Soviet Union were allies during World War II, they had different ideas about the future of the world. At the end of the war the Soviets controlled much of Eastern Europe and installed Communist governments there. The United States, on the other side, wanted to stop Communist ideas from spreading. It helped Western European countries to stay free and also gave them big sums of money to help rebuild their weak economies. The border between the Communist east and the free west was called the Iron Curtain and ran straight through the middle of Europe.