In order to understand the historical importance of the Berlin Wall, one needs to understand a little of the history of the Cold War, of which the Berlin Wall was the most recognized symbol.
Following the surrender of Nazi Germany, the leaders of the three victorious powers, the United States, Great Britain and the Soviet Union met in July 1945 at the German town of Potsdam. What became known as the Potsdam Conference involved the formal division of the defeated countries of Germany and Austria among the three participants, plus France. The division of Germany had already been agreed upon earlier in the year at a similar conference at the Crimean town of Yalta, inside the Soviet Union. The U.S. leader at Yalta, President Franklin Roosevelt, was frail from illness and would die the following month. The U.S. representative at Potsdam was Roosevelt's successor as president, Harry Truman. The British leader at Yalta, Prime Minister Winston Churchill, would soon be replaced by Clement Atlee, who represented his country at the July conference. The one constant among the leaders was Joseph Stalin, the brutal dictator of the Soviet Union.
As a result of the conferences, Germany was divided into four sectors, one each for the United States, Great Britain, France, and the Soviet Union. The city of Berlin, capital of Germany, would similarly be divided four-ways. As three of the four occupying powers were liberal democracies and the fourth, the Soviet Union, a totalitarian dictatorship, the division of Germany, and of Berlin, became more of a division into two halves, one free, the other captive to Joseph Stalin's political machinations.
Divided Berlin soon became the most dangerous potential flashpoint of the Cold War, until the Cuban Missile Crisis of October 1962 emerged as the closest the Cold War adversaries would come to nuclear war. The city of Berlin resided within what was now East Germany, and the Soviet Union harbored deep resentment at this Western presence within what it considered its sphere of influence. From June 1948 to May 1949, the Soviet Union maintained a blockade of West Berlin, allowing no supplies to be transported to the city by rail or truck. In response, the United States initiated Operation Vittles, the Berlin Airlift, during which it supplied the besieged city entirely by air.
In 1961, the Soviet Union surprised the West by initiating construction of a wall through the center of Berlin. This wall soon became the most potent symbol of the Cold War. Many East Germans died attempting to escape over, under or through the Berlin Wall over the following decades. The wall had the affect of stopping the flow of East Germans into West Berlin, a major source of embarrasment for the Soviet Union and its allies in East Germany. At the same time, the halt in the flow of refugees into West Berlin helped a West German government already burdened by the task of rebuilding following the devastation of World War II. The cost of absorbing East German refugees was high, and both halves of Germany were economically broke.
The Berlin Wall's fall in 1989 marked the end of the Cold War and the division of Europe into East and West.