What principle justifies the expansion of the U.S. across the American continents?

The belief that expansion was justified and inevitable is a critical principle that underpinned U.S. territorial growth, famously encapsulated in the concept of Manifest Destiny during the 19th century. This ideology posited that it was the Americans' divine right and destiny to expand their territory across North America, from the Atlantic to the Pacific Ocean. This belief was rooted in a combination of nationalism, the idea of American exceptionalism, and a perceived obligation to spread what they considered to be the advantages of American civilization, including democracy, liberty, and economic opportunity.

Manifest Destiny also had practical implications, as it encouraged the annexation of vast territories, including Texas, California, and the Oregon Territory. It fostered public support for policies that facilitated westward expansion, including the Indian Removal Act and the War with Mexico. Therefore, the belief that expansion was justified and inevitable not only reflects the mindset of the time but also directly influenced U.S. foreign and domestic policies throughout the 19th century.