The Cold War began after the defeat of Germany and Japan by the Allies in 1945. The alliance between the Anglo-Americans and the Union of Soviet Socialist Republics was based on their common hostility to Nazi Germany. That alliance began to unravel soon after Adolph Hitler committed suicide in 1945. The Cold War dominated world history for nearly fifty years.
Defeated Germany and Austria were divided into zones of occupation. The French, British, and Americans administered the West while the Soviets occupied the East. Berlin and Vienna were similarly occupied and divided. The two sides did not work well together. Germany was divided into a non-Communist West and a Communist East. Austria was made permanently neutral.
Europe was divided by an "iron curtain." Eastern Europe was turned into pro-Soviet Communist nations, and they formed the Warsaw Pact. Western Europe became democratic and pro-American, and it was united in the North Atlantic Treaty Organization (NATO).
Berlin was often the scene of tension during the Cold War. It was located deep within East Germany, so it was difficult for the West to maintain trade and communication links with West Berlin. The contest for control of this city led to the Berlin Airlift and the Berlin Wall.
In Asia, the Cold War was dominated by the Korean War (1950–1953) and the Vietnam War (1965–1973). The first conflict ended in a bloody stalemate and the second one ended in American defeat. Japan became a key American ally in the Cold War.
In the Middle East, the West supported Israel while the Soviets backed the Arabs. The two sides in the Middle East received weapons from their respective supporters. The Yom Kippur War (1973) between Israel and its neighbors almost led to a confrontation between Moscow and Washington.
Although the Cold War is over, there remains a great deal of tension between America and Russia.