How did NATO and the Warsaw Pact change Europe?

As World War II concluded, the Soviet Union began to seize territory in Eastern Europe as so-called "satellite states," causing the west to feel as though an "iron curtain" (a phrase popularized by Winston Churchill) had descended across Eastern Europe. In 1948, the Soviets closed off western-controlled West Berlin, which was surrounded by Soviet East Berlin and Soviet East Germany, to ground traffic. As a result, the Americans and their allies had to airlift supplies into West Berlin.

In 1949, in response to these events, NATO (the North Atlantic Treaty Organization) was formed. Countries in Western Europe and North America signed the agreement, which promised that they would come to each others' aid if attacked. Later, in 1952, Greece and Turkey also signed the agreement, as did West Germany in 1955.

In response, particularly to the alliance of West Germany with NATO, Eastern European countries and the Soviet Union signed the Warsaw Pact in 1955. East Germany was part of this pact, which effectively divided Europe into two competing alliance systems. The members of the Warsaw Pact also agreed to defend each other if one of them were attacked. In addition, the pact allowed the Soviet Union greater control over the member countries. For example, when the Soviets crushed the uprising in Hungary in 1956, they said they had carried it out through the Warsaw Pact. Effectively, NATO and the Warsaw Pact divided Europe into western-controlled and Soviet-controlled areas.