Short answers, pulled from the story.
President James Monroe first announced the doctrine on the 2nd of December 1823, during his seventh annual State of the Union address to Congress. The statement was not called the Monroe Doctrine until 1850, more than two decades after the speech.
The Monroe Doctrine was written chiefly by John Quincy Adams, who served as secretary of state under President Monroe and later became president himself. Monroe delivered the words in his address to Congress, but Adams is credited as the primary author of the document.
The United States lacked a credible navy and army when Monroe delivered the doctrine in 1823, so European powers had little reason to comply. For much of the 19th century, it was the British Royal Navy, acting in its own commercial interest, that enforced the doctrine's spirit rather than U.S. forces.
President Theodore Roosevelt added the Roosevelt Corollary in 1904, asserting the right of the United States to intervene in Latin American countries in cases of "flagrant and chronic wrongdoing" to prevent European creditors from doing so. It justified a wave of U.S. military occupations, including Haiti from 1915 to 1935 and Nicaragua in two separate periods between 1912 and 1933.
During the Cold War, the U.S. invoked the Monroe Doctrine to justify opposing Soviet influence in Latin America. President Kennedy cited it during the Cuban Missile Crisis in 1962 as grounds for confronting the Soviet Union over ballistic missiles on Cuban soil, and CIA director Robert Gates defended covert Contra operations in Honduras in 1984 using the same rationale.
The 2025 U.S. National Security Strategy announced a formal Trump Corollary to the Monroe Doctrine, calling on the United States to reassert and enforce the doctrine to restore American pre-eminence in the Western Hemisphere. After the capture of Venezuelan President Nicolás Maduro in a January 2026 raid, President Trump styled the action the "Donroe Doctrine" and declared that American dominance in the Western Hemisphere would never be questioned again.