Monroe's declaration of policy toward Europe did not become known as the Monroe Doctrine until about 30 years after it was proclaimed. In 1823, the U.S. was not powerful enough to enforce Monroe's proclamation. Outside the United States, the "doctrine" went mostly unnoticed.
In the early 1900s, the U.S. emerged as a world power and the Monroe Doctrine became the foundation of U.S. foreign policy. President Theodore Roosevelt added the "Roosevelt Corollary" to the Monroe Doctrine in 1904, which said the U.S. had the exclusive right to intervene in the affairs of Latin American countries that were actively involved in deliberate misconduct or that refused to pay their international debts.