Who Originally Enforced the Monroe Doctrine?

As one of the four core principles of the Monroe Doctrine, the president made it clear that European interference in the Western Hemisphere would be seen as hostile to American interests. However, he “did not lay out a plan of action should the Europeans ignore the warning, because in reality there wouldn’t be much the United States could do,” according to the National Museum of American Diplomacy.

In 1823, the United States lacked the ships, global reach and logistical capability to deter European intervention. According to Allan Stam, a political scientist and professor of public policy and politics at the University of Virginia, the United States was “militarily quite weak” at the time, whereas Britain had the world’s most powerful navy.

The U.S. and Britain had fought against each other in not one but two wars in the 40-odd years between the Revolution and the issuance of the Monroe Doctrine. Yet, by the 1820s, British interests, Stam says, were closely aligned with U.S. interests in keeping other European powers out of Latin America. In fact, earlier in 1823, the British foreign minister proposed the former foes team up on a nonintervention declaration that said as much.

“Napoleon arrives on the European continent and all of a sudden, both from Britain’s perspective and from America’s perspective, it makes a lot more sense for the British and the Americans to be essentially rowing in the same direction,” says Stam, who also serves as faculty senior fellow at UVA’s Miller Center. “So what looks like Great Britain enforcing [the Monroe Doctrine] for the United States is really Great Britain enforcing its interests.”

By the 1890s—especially after the Spanish‑American War—the U.S. had the military capacity and economic influence to enforce the Monroe Doctrine, according to the U.S. State Department. Just a decade later, the country used its newfound enforcement power in significant ways.

President Theodore Roosevelt’s 1904 Roosevelt Corollary marked a turning point in the doctrine’s interpretation by declaring the U.S. to be “policeman” of the Western Hemisphere. Under Roosevelt’s usage of the Monroe Doctrine, Stam says, the U.S. becomes “de facto imperialists.” Between 1904 and 1915, U.S. Marines were deployed to Santo Domingo (now the Dominican Republic), Nicaragua and Haiti, “ostensibly to keep the Europeans out,” according to the National Archives.