The American expansionists used the term "Manifest Destiny" to justify the belief that the United States had a God-given right and duty to spread their dominion across the continent to the Pacific Ocean.
This concept, developed in the mid-1800s, was mainly based on the belief that American people and their institutions had special virtues and potentialities, and therefore they had a duty to spread these institutions to redeem and remake the world in the image of the U.S., which was a high example; and that such task was given and protected by God.