The big turning point was the Spanish American War in 1898. While the United States had expanded across the continent as part of what became known as "Manifest Destiny" prior to that time, the country had nonetheless resisted the siren song of empire, which had long gripped European and Asian countries.

Through most of the 1800s, the U.S. government had a small-sized army and navy, which, for the most part, engaged in relatively small battles, such as against Indians, Barbary Pirates, and the Mexican army. The big exception was the Civil War, which entailed a massive military establishment, but one that was mostly dismantled at the conclusion of the war.

The founding foreign policy of the United States was summed up by people like George Washington, Thomas Jefferson, and John Quincy Adams: America would not enter into alliances with other countries, as European and Asian countries were prone to do, and it would not intervene in the wars, crises, and conflicts that occurred in foreign lands. America's role, they said, would be to build a model society of freedom here at home to serve as a model for the world — and also to serve as a sanctuary for people who escaped tyranny, oppression, or starvation around the world.