The Berlin Blockade of West Germany by the Soviet Union.
In June of 1948, the Soviet Union applied a blockade on Berlin to keep the others out. They didn't want to give up Eastern Germany or Eastern Berlin. The Soviets restricted access to the city in hopes that the Western allies would give up and give them Berlin. But the Western allies did not want to allow this. Especially the U.S. because we were so afraid of the Soviet Union and the spread of communism.