Expansionism: Expansionism refers to the policy or ideology of expanding a nation's territorial boundaries through various means. It often involves acquiring additional land or exerting influence over other regions.
Manifest Destiny: Manifest Destiny was the belief popularized in the 19th century that it was America's destiny and divine right to expand its borders from coast to coast, which influenced westward expansion efforts.
Treaty of Guadalupe Hidalgo: The Treaty of Guadalupe Hidalgo was an agreement signed between Mexico and the United States in 1848 after the Mexican-American War. It ceded large portions of Mexican-controlled territory (including present-day California, Nevada, Utah, Arizona, New Mexico, Colorado) to the United States.