The Anglo-American Bizonal Fusion Agreement of December 1946 embodied Russian concern about the consolidation of allied zones. The Soviet government, led by Stalin, feared a unitary Germany run by non-communist political parties. A conference of foreign ministers held at the end of 1947 failed to agree on future policy towards Germany.
Following the introduction a new currency in the western zones, from July 1948 Stalin deployed an embargo on rail and road traffic to Berlin from the west. The aim was to force an allied withdrawal from Berlin, and discredit western policy towards Germany. Truman was determined that the allies should stay in Berlin and used an airlift to provide the city with food and fuel. Stalin called off the blockade in May 1949 having failed in his objectives. Another conference of foreign ministers failed to produce an agreement.
The blockade heightened the tensions of the Cold War. It greatly increased concerns about the vulnerability of Western Europe to an attack by Stalin's forces. In the Brussels Treaty of March 1948, Britain, France, the Netherlands, Belgium and Luxembourg agreed mutual assistance in the event of an attack.
On its own the pact was too weak to deter the Soviet Union from aggression but the Berlin blockade had, by now, convinced the US that Russia was a serious threat. The Vandenberg Resolution of June 1948 enabled the US to enter into military treaties with foreign states, and in April 1949, the United States, Canada, the Brussels powers, and most of the other Western European nations signed the North Atlantic Treaty, agreeing to mutual defence in the event of an attack by the Soviet Union. The North Atlantic Treaty Organisation (NATO) was formed.
At the outbreak of the Korean War in 1950, the US and Russia headed two opposing power blocs. This high state of tension and conflict became known as the Cold War, and was a major feature of global international relations in following years.