The Monroe Doctrine, a significant piece of United States foreign policy, was first articulated by President James Monroe in 1823, and it essentially warns the powers of Europe from meddling in the affairs of the Western Hemisphere, claimed by the US as its own sphere of influence. Initially, the doctrine was meant to oppose European colonialism while simultaneously asserting the US as a rising regional power. By the turn of the 20th century, it had taken on a new meaning and was often used as justification for the 'policing' of Latin America by the US. Since its inception, the Monroe Doctrine has routinely been invoked to justify various US foreign policy positions and remains relevant today.

Towards the end of the Napoleonic Wars (1803 to 1815), a wave of revolutions swept across Latin America. Spain had been ravaged by the armies of Napoleon I (reign 1804 to 1814; 1815) and could barely afford to keep control over its colonial empire in the Americas, a weakness that liberty-seeking revolutionaries managed to exploit. Under the leadership of men like Simón Bolívar (1783 to 1830) and José de San Martín (1778 to 1850), the revolutionaries cast off the shackles of Spanish colonial rule and established independent republics based on the ideals of the Enlightenment. But even then, with the taste of victory still on their lips, it was clear that these republics' grasp on independence was tenuous at best. As the great European powers rallied and rebuilt after the downfall of Napoleon, it was clear that it would be only a matter of time before they turned their imperialist eyes back West, toward the lost colonies of the Americas.

Indeed, plans to recolonize the New World were already materializing in the Old. Austria, Prussia, and Russia – three of the victors in the wars against Napoleon – sought to cleanse the world of radical Enlightenment ideals and restore the kind of absolute monarchism that had been the status quo before the French Revolution (1789 to 1799) had turned the world upside down. These empires formed a coalition called the Holy Alliance and vowed, among other things, to return the Bourbon Dynasty to the Spanish throne and resubjugate the Latin American peoples to Spanish domination. Naturally, this worried the fledgling republics, which knew that they could do little to resist a European incursion upon their shores. Fortunately, there seemed to be two stronger nations that opposed the Holy Alliance and might be able to help.

The first of these potential allies was Great Britain, then the foremost world power. A constitutional monarchy, Britain was ideologically opposed to the absolutist empires of the Holy Alliance. Moreover, the British had spent years cultivating a lucrative market for trade in South America and would be loath to see these eager customers fall back under Spanish rule. The other nation, of course, was the United States. Another republic founded on Enlightenment ideals, the US had won its own independence barely half a century earlier and would not stand to see absolutism take root in its own backyard. Less altruistically, the US dreamt of expanding its own empire ever westward – an "empire of liberty" as Thomas Jefferson once put it – which would eventually put it at odds with Russia, which had long laid claim to the Pacific Coast, and a post-Napoleonic France, which was eyeing its own return to the Americas. If the US could not prevent European recolonization, it may as well kiss its own imperialist dreams goodbye.

Seeing as both Britain and the US opposed the Holy Alliance's intervention in Latin America, it seemed sensible for them to make common cause. Indeed, British Foreign Minister George Canning offered to do exactly that and proposed that the two nations issue a joint statement warning the Holy Alliance to stay out of the Americas. At first, US President James Monroe (served 1817 to 1825) thought this was a good idea, but he was soon dissuaded by his secretary of state, John Quincy Adams (1767 to 1848). A shrewd diplomat, Adams understood that by making a joint statement, the US would be perceived as merely a junior partner doing the bidding of Britain. But if the US were to issue a statement on its own, it would be asserting its authority in the Western Hemisphere and would be claiming the status of a rising power. "It would be more…dignified," Adams wrote, "to avow our principles explicitly to Russia and France then to come in as a cockboat in the wake of the British man-of-war" (quoted in Crandall & Crandall). Monroe, ultimately, agreed.

On 2 December 1823, President Monroe made his annual address to Congress, in which he articulated the doctrine that would, forever after, bear his name. The words, of course, were Adams's, as were many of the ideas behind them; indeed, it would not be far off the mark to say that Adams ghostwrote the doctrine. The Monroe Doctrine was certainly lengthy, but as historian Daniel Walker Howe explains, its essence can be boiled down into four main points. The first – and most important – is the declaration that, from now on, both North and South America are off limits to European interference. Monroe made it clear that the US would not tolerate "future colonization by any European power" anywhere in the Americas (quoted in Howe, 115).

Secondly, Monroe proclaimed that the US would regard any European intervention as "dangerous to our peace and safety," an implicit threat of military action should the doctrine be ignored (ibid). The third point was a concession to Europe, as well as a throwback to the isolationist policies of George Washington – if the Europeans stayed out of the Americas, Monroe promised that the US would not meddle in Europe's affairs. Monroe clarified that this meant the US would stay neutral in European wars as well as Europe's "internal concerns." Finally, the doctrine forbade Spain from transferring any of its existing colonial possessions to other European powers. This last "no-transfer principle" did not actually make it into Monroe's speech, but it was nevertheless important to the spirit of the doctrine. Thus, Monroe had articulated the doctrine – whether the US had the power to back up his words and stand up to the might of Europe remained to be seen.

The Monroe Doctrine was initially celebrated by the fragile republics of Latin America. Indeed, Colombian revolutionary hero Francisco de Paula Santander wrote that "this policy, consolatory to human nature, would secure Colombia a powerful ally should its independence and liberty be menaced by Allied powers" (quoted in Crandall & Crandall). Simón Bolívar, too, recognized the value of US friendship – skeptical of it though he may have been – and invited US representatives to attend the 1826 Panama Conference of American republics. Even still, most Latin Americans understood that the US lacked the military power to stand up to Europe and considered the doctrine to be little more than a symbolic resolution.

The first test would come in 1833, and, somewhat ironically, the offender was none other than Britain. Royal Navy warships seized control of the Falkland Islands (Islas Malvinas) from Argentina in direct violation of the doctrine, but the US, unable to contest British naval power, did nothing. Then, beginning in 1838, the Río de la Plata of Argentina was blockaded first by the French, then by the British; again, the US failed to respond. This did not mean that the US had forgotten the Monroe Doctrine – just that it was picking and choosing where to apply it. In 1845, President James K. Polk (served 1845 to 1848) invoked the doctrine in his bid to wrest the Oregon Territory from British control. A fervent believer in manifest destiny, Polk offered a new interpretation of the doctrine. Whereas it had originally been meant only to keep Europe out of the Americas, Polk now used it as justification for the US expansion into the West.

In 1862, the doctrine faced its most significant test yet, when forces under French Emperor Napoleon III (reign 1852 to 1870) invaded and conquered Mexico, establishing a puppet regime. At the time, the US was preoccupied with the American Civil War (1861 to 1865) and could do nothing to oppose the move militarily, but the Lincoln Administration still loudly condemned this French incursion into the New World. In 1865, after the Civil War had ended, the US sent an army to the border with Mexico to demand that France withdraw its troops. Partially because of this pressure, Napoleon III assented and evacuated his soldiers in 1867, abandoning his puppet government to its fate – Maximilian I, the Habsburg prince that Napoleon had installed as Emperor of Mexico, was then captured by Mexican republicans and executed by firing squad. US Secretary of State William H. Seward chalked this up to a successful application of the doctrine, declaring that the "Monroe Doctrine, which eight years ago was merely a theory, is now an irreversible fact" (quoted in Maass, 154).

As the power of the US grew in the second half of the 19th century, its application of the Monroe Doctrine became ever bolder. In 1870, President Ulysses S. Grant (served 1869 to 1877) invoked the doctrine in his failed bid to annex the Dominican Republic. It was invoked again in 1895, when US officials intervened in a territorial dispute between Britain and Venezuela. However, it was most consequentially used to justify the Spanish-American War of 1898, when the US sided with rebels in Cuba and went to war with Spain. That war lasted less than half a year and ended with the US annexation of Puerto Rico, the Philippines, and Guam, as well as Cuba ending up as a US protectorate. The doctrine, therefore, was no longer just a symbolic protestation of European colonialism, but a mandate for the US to cast its shadow across the entire Western Hemisphere.

The way that the Monroe Doctrine was applied to international affairs underwent a major shift in the first years of the 20th century. The trouble began with Venezuela, which had borrowed considerable sums of money from Britain, Italy, and Germany but was unable to pay them back. Frustrated, these European powers responded aggressively, jointly blockading Venezuela with gunboats in 1902 to 03. Though the US responded with a show of naval force and an offer to mediate, it played little role in ending the crisis. Indeed, the situation was only de-escalated when an international court stepped in and ruled that Britain, Italy, and Germany were entitled to preferential treatment when acquiring the debts owed by Venezuela.

Though the conflict had been resolved, this development was nonetheless deeply worrying to US President Theodore Roosevelt (served 1901 to 1909). The presence of European warships in American waters, and indeed the ruling of the international court in favor of Britain, Italy, and Germany, threatened to undermine US influence in the Western Hemisphere. After all, if the European powers could settle disputes with Latin American nations without US involvement, what was the point of the Monroe Doctrine? Roosevelt opted to solve this problem by issuing a new amendment to the Monroe Doctrine, which he articulated in his annual address to Congress in December 1904.

This amendment, known as the Roosevelt Corollary, once again told European powers to stay out of American affairs. In return, Roosevelt promised that the US would act as the international 'police force' of the Western Hemisphere and would maintain order in Latin America. This meant that the next time a Latin American nation owed money to Europe, it would be the responsibility of the US to force it to pay up. The wording of the corollary was such that the US could intervene anytime it believed a Latin American nation was acting in violation of international law. "Brutal wrongdoing," Roosevelt declared, "or an impotence which results in a general loosening of the ties of civilizing society may finally require intervention by some civilized nation…The United States," he concluded, "cannot ignore this duty" (quoted in Leonard, 789).

The Roosevelt Corollary, therefore, fundamentally redefined the Monroe Doctrine. Rather than merely keeping the European powers out of the Americas, the US was now claiming the entire Western Hemisphere as its sphere of influence. Indeed, the US took advantage of its self-proclaimed role as sheriff of the Americas. The two decades that followed Roosevelt's amendment saw direct US military intervention in the affairs of eight countries: Cuba, the Dominican Republic, Guatemala, Haiti, Honduras, Mexico, Nicaragua, and Panama. US marines were stationed in some of these nations long-term to safeguard the collection of customs revenue, despite outcry from across Latin America. Under the thin veil of the Monroe Doctrine, the US now seemed uncomfortably similar to the imperialist powers that, a century before, it had promised to protect Latin America from.

The wave of US interventionism unleashed by the Roosevelt Corollary did not subside until 1933, during the presidency of another Roosevelt. The Good Neighbor Policy, implemented by President Franklin D. Roosevelt (served 1933 to 1945), followed the principle of non-intervention in the domestic affairs of Latin America. Hoping to prove that the US was a "good neighbor" to the nations down south, FDR sought to create stronger ties with Latin America and promote new economic opportunities and trade agreements. The Latin American nations were understandably skeptical of the Good Neighbor Policy, but, true to his word, FDR did not intervene militarily in Latin America for the remainder of his presidency. He did, however, invoke the Monroe Doctrine after the outbreak of the Second World War (1939 to 1945) when he sent troops to occupy Greenland.

The Good Neighbor Policy did not long outlive FDR's presidency. The outbreak of the Cold War (1947 to 1991) once again saw the US look to intervene in Latin America – only, this time, it was the specter of Communism, rather than that of European colonization, that it meant to combat. In 1954, US Secretary of State John Foster Dulles invoked the doctrine to warn the Soviet Union to stay out of Guatemala. In 1962, President John F. Kennedy (served 1961 to 1963) referenced the doctrine during the Cuban Missile Crisis, using it as part of his reasoning why the Soviets must not be allowed to install ballistic nuclear missiles in Cuba.

Afterward, although the doctrine was rarely mentioned by name, its spirit was very much alive and well, as the US continued to intervene – oftentimes discreetly – in the domestic affairs of Latin America. Far from being a relic of the past, the Monroe Doctrine has been continually invoked during the 21st century as well. Indeed, at the time of writing, it was most recently invoked by the second Trump Administration as justification for US military action in Venezuela in January 2026.

In terms of US foreign policy, the Monroe Doctrine remains alive and well, ever shifting to fit in with the times. It began as a largely symbolic statement, issued by the president of a second- or third-rate power, with little bite to back up his bark. Gradually, as the power of the US increased, the purpose of the Monroe Doctrine changed. By the turn of the 20th century, it no longer merely protected Latin America from European colonization but also gave the US free rein to police the Western Hemisphere as it pleased. After 200 years, the doctrine remains a landmark piece of US foreign policy, likely to stick around in some way, shape, or form for as long as the US remains a global superpower.