Basically, that Europe (or anyone) shouldn't mess with the Western hemisphere, and in return the US won't mess with European colonies.
Andrea Pitzer explains:
"Under the Monroe Doctrine, established two centuries ago, the U.S. claimed a right to block foreign governments from influencing the leadership and policies throughout the Americas. The doctrine was established in the face of the the expanding independence of many countries in the the Western Hemisphere.
A century after the Monroe Doctrine was announced, Teddy Roosevelt expanded it, claiming via the Roosevelt Corollary that even beyond preventing European interference, the United States also had a responsibility to preserve order and protect life and property in the hemisphere.
In 1933, FDR shifted the century-old policy by emphasizing collaboration over military intervention, instituting his Good Neighbor Policy. But during the Cold War, the threat of global communism was seen as justifying the kind of interventions that had been widespread before. Across the twentieth century as a whole the U.S. interfered to install or directly support dozens of dictators in the Americas."
Heather Cox Richardson, December 5, 2025 says:
"President James Monroe outlined what became known as the Monroe Doctrine in three paragraphs in his annual message to Congress on December 2, 1823. The concept was an attempt for the new American nation to position itself in a changing world.
In the early nineteenth century, Spain’s empire in America was crumbling, and beginning in 1810, Latin American countries began to seize their independence. In just two years from 1821 to 1822, ten nations broke from the Spanish empire. Spain had restricted trade with its American colonies, and the U.S. wanted to trade with these new nations. But Monroe and his advisors worried that the new nations would fall prey to other European colonial powers, severing new trade ties with the U.S. and orienting the new nations back toward Europe.
So in his 1823 annual message, Monroe warned that “the American continents, by the free and independent condition which they have assumed and maintain, are henceforth not to be considered as subjects for future colonization by any European powers.” American republics would not tolerate European monarchies and their system of colonization, he wrote. Americans would “consider any attempt on their part to extend their system to any portion of this hemisphere as dangerous to our peace and safety.” It is “the true policy of the United States to leave the [new Latin American republics] to themselves, in hope that other powers will pursue the same course,” Monroe wrote."
Wikipedia, accessed 7 Jan 2026, says:
"The Monroe Doctrine is a United States foreign policy position that opposes European colonialism in the Western Hemisphere which since WWII has been extended to oppose any foreign interference in the Western Hemisphere. It holds that any intervention in the political affairs of the Americas by foreign powers is a potentially hostile act against the United States. The doctrine was central to American grand strategy in the 20th century.
President James Monroe first articulated the doctrine on December 2, 1823, during his seventh annual State of the Union Address to Congress (though it was not named after him until 1850). At the time, nearly all Spanish colonies in the Americas had either achieved or were close to independence. Monroe asserted that the New World and the Old World were to remain distinctly separate spheres of influence, and thus further efforts by European powers to control or influence sovereign states in the region would be viewed as a threat to U.S. security. In turn, the United States would recognize and not interfere with existing European colonies nor meddle in the internal affairs of European countries."
Read also: Trump Strategy Document Revives The 19th Century Monroe Doctrine: The United States has sent more than 10,000 troops to the Caribbean, along with an aircraft carrier, warships and fighter jets. Idrees Ali, Matt Spetalnick and James Mackenzie,
Reuters, on HuffPost, Dec 6, 2025
Read also: The U.S. Plan to Pillage Latin America is Becoming Clearer: Trump Administration officials have frequently invoked the Monroe Doctrine, explaining the aggression toward Latin America, Arturo Dominguez, Oct 20, 2025
Read also: The Old Order is Over, Nadin Brzezinski, Dec 6, 2025
"Observers referred to the document as National Security Council Report (NSC) 88 and noted that it could have been written in just 14 words. White supremacists use 88 to refer to Adolf Hitler and “fourteen words” to refer to a popular white supremacist slogan."
— Heather Cox Richardson, December 5, 2025
..jpg){kind=link}