The concept that justified American expansion across the continent is known as?

• A. The Monroe Doctrine
• B. The Open Door Policy
• C. Manifest Destiny
• D. The Truman Doctrine

Answer: (C)

Manifest Destiny is the belief that the United States was destined to expand its territory across North America, spreading democracy and civilization. This idea gave people a justification and motivation to move west, acquire new lands, and bring American institutions from the Atlantic to the Pacific. It fits best because it directly describes why many Americans supported continental expansion. The Monroe Doctrine focuses on keeping European powers out of the Western Hemisphere, not on expanding U.S. land itself. The Open Door Policy deals with trade in China, and the Truman Doctrine concerns containing communism after World War II, so neither explains why Americans argued for westward growth.