Which belief justified westward expansion in the 1800s?

• A. Manifest Destiny.
• B. Isolationism.
• C. Mercantilism.
• D. Feudalism.

Answer: (A)

Manifest Destiny—the belief that the United States was destined to spread across North America, guided by a sense of mission and divine sanction—drove westward expansion in the 1800s. This idea provided moral justification and political momentum for expanding territory, fueling actions from the annexation of Texas and settlement of Oregon to the Mexican‑American War and the vast lands acquired as a result. It framed expansion as inevitable and beneficial for democracy and liberty, even as it often displaced Indigenous peoples. Isolationism would pull the nation away from continental growth, mercantilism centers on trade relations and colonial wealth rather than a territorial destiny, and feudalism is a medieval system unrelated to U.S. policy in this era.