The Berlin Blockade was the first major international crisis of the Cold War. After the end of World War II, the Allies divided Germany into administrative zones, with the USSR retaining control of eastern Germany, approximately up to the line of the Soviet Army at the time the war ended, while France, England, and the US retained control of individual administrative zones in western Germany. Each country was given responsibility for governing a zone of the country, while Berlin was likewise divided into zones for each of the Allied countries. Unfortunately, Berlin was deep inside the Soviet zone of administration, making it an isolated outpost for the Western nations.

Tensions began rising as hostility between the USSR and the Western nations increased. Europeans feared the advance of the Soviet army, and Stalin was wary of being surprised by another ally (the USSR was initially invaded by Germany despite a non-aggression pact between the two). France, England, and the US began planning for the unification of their respective zones into West Germany. The USSR discovered this and withdrew from the Allied governing council for Germany. The Western Allies began working toward political and economic changes among the West German administrative zones, and, in the summer of 1948, the Deutschmark was introduced to West Berlin in an attempt to gain economic control over these areas.

The USSR responded by blockading road and rail lines from West Germany into West Berlin and by introducing its own currency, the Ostmark. The blockade was a gamble to gain exclusive control over West Berlin, the idea being that West Berlin was too small for the Western Allies to risk overt hostilities or the use of a nuclear weapon, especially considering the relative sizes of the Soviet and Western armies. Stalin likely thought the West's desire to avoid hostilities would force them to cede control of West Berlin to the USSR because the West would be unable to provide supplies.

The US and its allies made a similar calculation about the USSR's desire to avoid open conflict. Based on this calculation, an airlift was organized to supply West Berlin, forcing the USSR to either allow the supplies or to use force against an unarmed humanitarian mission. This stalemate lasted for almost a year.

The result of the blockade and airlift was the solidification of the division of Europe and the development of NATO.

In many ways the blockade was a challenge from Stalin to Western Europe and the allied powers of the United States and England and the other Western European governments.  Stalin felt that the Allies would not be interested in spending the enormous amounts of resources necessary to maintain their presence in West Berlin and would simply cede the city over to their control.

Of course the allies felt differently and embarked on an enormous effort to bring everything necessary to Berlin by air, generally loads of up to 1500 tons a day.  This included food, heating fuel or coal, even materials to build a larger runway.  The effort was a great morale booster for the allies and also helped to cement the ties with the new German government by showing that the allies would go to great lengths to maintain the integrity of their new borders and keep them safe from what they saw as the Soviet threat.