Missions:
The belief that non-Christians were uncivilized and needed to be protected, so they often sent people on missions to Africa and Asia to "fix" them.
Militarism:
By taking over foreign territories with strong militaries they were able to expand and protect those territories.
Social Darwism and Jingoism:
Many U.S. politicians and businesspeople wanted to prove the nation’s military strength and superiority to the rest of the world. Many held an attitude that came to be known as jingoism.
Economic Motives:
U.S. politicians, bankers, manufacturers, and others believed the young nation must expand its markets and its influence. They thought that if the country failed to compete in the international free market, it would lose out to the European powers.
Frontier Thesis:
U.S. politicians, bankers, manufacturers, and others believed the young nation must expand its markets and its influence. They thought that if the country failed to compete in the international free market, it would lose out to the European powers.
It's called that because they adopted previous Manifest Destiny ideals and applied them to the expansion of america across seas.