Arthur Hendrick Vandenberg Sr. was an American politician who served as a United States senator from Michigan from 1928 to 1951. A member of the Republican Party, he participated in the creation of the United Nations. He is best known for leading the Republican Party from a foreign policy of isolationism to one of internationalism, and supporting the Cold War, the Truman Doctrine, the Marshall Plan, and NATO. He served as president pro tempore of the United States Senate from 1947 to 1949.

The Truman Doctrine is an American foreign policy that pledges American "support for democracies against authoritarian threats." The doctrine originated with the primary goal of countering the growth of the Soviet bloc during the Cold War. It was announced to Congress by President Harry S. Truman on March 12, 1947, and further developed on July 4, 1948, when he pledged to oppose the communist rebellions in Greece and Soviet demands from Turkey. More generally, the Truman Doctrine implied American support for other nations threatened by Moscow. It led to the formation of NATO in 1949. Historians often use Truman's speech to Congress on March 12, 1947 to date the start of the Cold War.