Which concept emphasizes the expansion of U.S. borders during the 19th century as both a right and duty?

The concept that emphasizes the expansion of U.S. borders during the 19th century as both a right and a duty is Manifest Destiny. This idea was rooted in the belief that it was the United States' divine obligation to expand its territory across the North American continent. Proponents of Manifest Destiny argued that this expansion was not only a right based on the nation's perceived superiority and virtues but also a moral imperative that would spread democracy and civilization.

Manifest Destiny played a significant role in motivating territorial acquisitions such as the annexation of Texas, the Oregon Trail migration, and the Mexican-American War. The term itself encapsulates the spirit of the time, illustrating how expansion was justified as a natural and positive development for both the nation and the people living in those areas.

American Expansionism does share similarities with Manifest Destiny but lacks the specific moral and philosophical connotations associated with the latter. Colonialism and Western Imperialism pertain to broader concepts of domination and control over foreign territories but do not specifically focus on the belief in a destined or obligatory expansion of U.S. borders.