The Monroe Doctrine, put forth by President James Monroe in 1823, was the foundation for the Roosevelt Corollary of 1904. President Monroe announced his policy as a unilateral American response to Britain's overtures. Specifically, Britain was concerned that the Holy Alliance (Austria, Prussia, and Russia) would help Spain recover its lost colonies in the Americas. The Monroe Doctrine proclaimed that the Americas were off limits to any further colonization. In fact, the US was too weak to enforce its proclamation, and it was enforced by the British navy.
The Monroe Doctrine was not invoked very often during the nineteenth century. The biggest challenge to it was Napoleon III's intervention in Mexico during the US Civil War (1861–1865). After 1865, Washington sent troops to the Texas frontier and warned France to get out of Mexico. In 1895, President Grover Cleveland appealed to the Monroe Doctrine in the Venezuela Claims controversy.
President Theodore Roosevelt's Corollary to the Monroe Doctrine was a major enhancement and strengthening of previous American policy. Roosevelt was an imperialist who was instrumental in America's decision to construct a large navy. Because of its new navy and greater national power, the US acted more aggressively in Latin America. In the late nineteenth century, European nations had colonized almost all of Africa. Roosevelt was determined not to allow them to do the same in Latin America.
Roosevelt's Corollary was nothing less than a justification of US intervention in the affairs of other American nations. For example, in 1905, the Dominican Republic was indebted to Europe, and Roosevelt intervened in that nation to forestall European involvement there. Further American invasions of Latin America occurred in Nicaragua in 1912 and in Haiti in 1915. President Woodrow Wilson continued Theodore Roosevelt's aggressive posture in Latin America.
President Franklin Delano Roosevelt introduced the Good Neighbor policy in the 1930s and American troops were withdrawn. FDR also sought close cooperation with Latin America during World war II (1939–1945).
However, American interventionism in Latin America frequently occurred during the Cold War (1947–1991).
Today, imperialism is widely regarded as unjustified aggression toward weaker nations. Because the Roosevelt Corollary led to Washington's imperialism in the Americas, it cannot be defended.