As a Wilsonian internationalist, Truman supported Roosevelt's policy in favor of the creation of the United Nations and included Eleanor Roosevelt on the delegation to the UN's first General Assembly.
With the Soviet Union expanding its sphere of influence through Eastern Europe, Truman and his foreign policy advisors took a hard line against the USSR.
In this, he matched U.S. public opinion which quickly came to believe the Soviets were intent upon world domination.

Although he had little personal expertise on foreign matters, Truman listened closely to his top advisors, especially George Marshall and Dean Acheson.
The Republicans controlled Congress in 1947–1948, so he worked with their leaders, especially Senator Arthur H. Vandenburg, chairman of the powerful Foreign Relations Committee.
He won bipartisan support for both the Truman Doctrine, which formalized a policy of Soviet containment, and the Marshall Plan, which aimed to help rebuild postwar Europe.

To get Congress to spend the vast sums necessary to restart the moribund European economy, Truman used an ideological argument, arguing that communism flourishes in economically deprived areas.
As part of the U.S. Cold War strategy, Truman signed the National Security Act of 1947 and reorganized military forces by merging the Department of War and the Department of the Navy into the National Military Establishment (later the Department of Defense) and creating the U.S. Air Force.
The act also created the CIA and the National Security Council.
In 1952, Truman secretly consolidated and empowered the cryptologic elements of the United States by creating the National Security Agency (NSA).

Truman did not know what to do about China, where the Nationalists and Communists were fighting a large-scale civil war.
The Nationalists had been major wartime allies and had large-scale popular support in the United States, along with a powerful lobby.
General George Marshall spent most of 1946 in China trying to negotiate a compromise, but failed.
He convinced Truman the Nationalists would never win on their own and a very large-scale U.S. intervention to stop the Communists would significantly weaken U.S. opposition to the Soviets in Europe.
By 1949, the Communists under Mao Zedong had won the civil war, the United States had a new enemy in Asia, and Truman came under fire from conservatives for "losing" China.
As a Wilsonian internationalist, Truman supported Roosevelt's policy in favor of the creation of the United Nations and included Eleanor Roosevelt on the delegation to the UN's first General Assembly. With the Soviet Union expanding its sphere of influence through Eastern Europe, Truman and his foreign policy advisors took a hard line against the USSR. In this, he matched U.S. public opinion which quickly came to believe the Soviets were intent upon world domination.
Although he had little personal expertise on foreign matters, Truman listened closely to his top advisors, especially George Marshall and Dean Acheson. The Republicans controlled Congress in 1947–1948, so he worked with their leaders, especially Senator Arthur H. Vandenburg, chairman of the powerful Foreign Relations Committee. He won bipartisan support for both the Truman Doctrine, which formalized a policy of Soviet containment, and the Marshall Plan, which aimed to help rebuild postwar Europe.
To get Congress to spend the vast sums necessary to restart the moribund European economy, Truman used an ideological argument, arguing that communism flourishes in economically deprived areas. As part of the U.S. Cold War strategy, Truman signed the National Security Act of 1947 and reorganized military forces by merging the Department of War and the Department of the Navy into the National Military Establishment (later the Department of Defense) and creating the U.S. Air Force. The act also created the CIA and the National Security Council. In 1952, Truman secretly consolidated and empowered the cryptologic elements of the United States by creating the National Security Agency (NSA).
Truman did not know what to do about China, where the Nationalists and Communists were fighting a large-scale civil war. The Nationalists had been major wartime allies and had large-scale popular support in the United States, along with a powerful lobby. General George Marshall spent most of 1946 in China trying to negotiate a compromise, but failed. He convinced Truman the Nationalists would never win on their own and a very large-scale U.S. intervention to stop the Communists would significantly weaken U.S. opposition to the Soviets in Europe. By 1949, the Communists under Mao Zedong had won the civil war, the United States had a new enemy in Asia, and Truman came under fire from conservatives for "losing" China.
Harry S. Truman