Final answer:
U.S. President Harry Truman defined the world in a binary of democracy versus communism through the Truman Doctrine. The U.S. assumed the role of containing communism globally and promoting democracy, often intervening in foreign nations during the Cold War.
Step-by-step explanation:
U.S. President Harry Truman defined the world in a binary of democracy versus communism, initiating what became known as the Truman Doctrine. President Truman suggested that the United States should assume the role of a global leader in the fight against the spread of communism. This was particularly evident with the United States providing military aid to Greece and Turkey to prevent the rise of communist governments in these countries. The Truman Doctrine essentially declared that the U.S. would support free peoples resisting subjugation by armed minorities or external pressures, namely communist expansions.
The United States continued to assume a role of promoting democracy and containing communism throughout the Cold War, often intervening in foreign nations to assert its interests and support non-communist regimes. This included the controversial decision to enter the Korean War without a formal declaration of war by Congress, thereby expanding presidential authority in foreign policy matters significantly.