Soviets blockade West Berlin

On June 24, 1948, the Soviet Union began the West Berlin Blockade by stopping access by road, rail, and water. From the article:

"Soviets blockade West Berlin
One of the most dramatic standoffs in the history of the Cold War begins as the Soviet Union blocks all road and rail traffic to and from West Berlin. The blockade turned out to be a terrible diplomatic move by the Soviets, while the United States emerged from the confrontation with renewed purpose and confidence.

Following World War II, Germany was divided into occupation zones. The United States, Great Britain, the Soviet Union, and, eventually, France, were given specific zones to occupy in which they were to accept the surrender of Nazi forces and restore order. The Soviet Union occupied most of eastern Germany, while the other Allied nations occupied western Germany. The German capital of Berlin was similarly divided into four zones of occupation. Almost immediately, differences between the United States and the Soviet Union surfaced. The Soviets sought huge reparations from Germany in the form of money, industrial equipment, and resources. The Russians also made it clear that they desired a neutral and disarmed Germany. The United States saw things in quite a different way. American officials believed that the economic recovery of Western Europe was dependent on a strong, reunified Germany. They also felt that only a rearmed Germany could stand as a bulwark against Soviet expansion into Western Europe. In May 1946, the Americans stopped reparations shipments from their zone to the Soviets. In December, the British and Americans combined their zones; the French joined some months later. The Soviets viewed these actions as a threat and issued more demands for a say in the economic future of Germany. On June 22, 1948, negotiations between the Soviets, Americans, and British broke down. On June 24, Soviet forces blocked the roads and railroad lines into West Berlin.

American officials were furious, and some in the administration of President Harry S. Truman argued that the time for diplomacy with the Soviets was over. For a few tense days, the world waited to see whether the United States and Soviet Union would come to blows. In West Berlin, panic began to set in as its population worried about shortages of food, water, and medical aid. The United States response came just two days after the Soviets began their blockade. A massive airlift of supplies into West Berlin was undertaken in what was to become one of the greatest logistical efforts in history. For the Soviets, the escapade quickly became a diplomatic embarrassment. Russia looked like an international bully that was trying to starve men, women, and children into submission. And the successful American airlift merely served to accentuate the technological superiority of the United States over the Soviet Union. On May 12, 1949, the Soviets officially ended the blockade."