The Berlin Airlift could be considered a pivotal event of the Cold War, precisely because of its symbolic effects on the relationship between the United States, West Germany, and the Soviet Union. The airlift was an American and British response to a crisis that emerged in 1948. Desiring to unite West Berlin and East Berlin under communist rule, Soviet leader Joseph Stalin ordered that roads into West Berlin from West Germany (occupied by the United States and Great Britain) be sealed off. The United States did not want to risk war with the Soviets by attempting to breach the blockade, and so American and British planes flew in an enormous quantity of supplies during the years 1948-49 (airports in West Berlin remained open.) This enabled West Berlin to see out the blockade, which Stalin lifted in May of 1949. The incident demonstrated to the Soviets (and the West German people) that the United States was unwilling to give in on the issue of West Berlin. The city remained the epicenter of Cold War tensions, lurching from one crisis to the next, until the early 1960s, when Soviet leader Nikita Khrushchev and the East Germans ordered the construction of a wall separating East Berlin from the West.