What was the main idea behind Manifest Destiny?

The main idea behind Manifest Destiny is centered around the belief in U.S. expansion across North America. This 19th-century doctrine held that the expansion of the United States throughout the American continents was both justified and inevitable. Proponents of Manifest Destiny believed that it was the nation's destiny to expand its territory and spread its form of democracy and civilization from the Atlantic Ocean to the Pacific Ocean.

This ideology not only encouraged the acquisition of new lands, such as Texas and California, but it also fostered a sense of American exceptionalism, suggesting that the U.S. had a divine right and mission to expand. The notion often resulted in significant consequences for Native American populations and other nations, as territories were taken or claimed without regard to the existing inhabitants.

The other choices do not encapsulate the essence of Manifest Destiny. Establishing a centralized government relates to political structures rather than territorial expansion. The promotion of international diplomacy suggests a focus on foreign relations, which contrasts with the domestic focus of Manifest Destiny. Preservation of Native American lands directly opposes the central tenet of Manifest Destiny, which typically led to the displacement of Native peoples in favor of American settlers.