8 US Military Interventions of the 20th Century & Why They Happened

After the Spanish-American War in 1898, the US military flexed its muscles throughout the 20th century with several small-scale foreign interventions.

Oct 22, 2022By Owen Rust, MA Economics in progress w/ MPA

list of us military interventions 20th century


In 1823, US President James Monroe declared that European imperial powers should stay out of the Western Hemisphere in what is now known as the Monroe Doctrine. Seventy-five years later, the US used its industrialized muscle to back up the doctrine in the lightning-fast Spanish-American War. Victorious over Spain in 1898, the US spent the next century flexing its own imperial muscles by intervening militarily in several less well-known conflicts. While most graduates of high school history classes know about the World Wars and wars in Korea, Vietnam, and the Persian Gulf, here is a look at eight other important US military interventions during the 20th century.


Setting the Stage: 1823 & the Monroe Doctrine

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A political cartoon praising the Monroe Doctrine as protecting Central and South America from European imperialism, via the Library of Congress, Washington DC


In 1814, the United States held off the military might of Great Britain and secured its independence at the conclusion of the War of 1812. Concurrently with the War of 1812, French dictator Napoleon Bonaparte had been rampaging throughout continental Europe, including Spain. With the Spanish crown under the control of Napoleon, Spain’s colonies in Mexico and South America began independence movements. Although Napoleon was finally defeated in 1815 and Spain permanently regained its sovereignty, the colonial independence movements continued. Between 1817 and 1821, Spain’s viceroyalties became independent nations.


One of the new nations, Mexico, bordered the United States and gained its independence in 1821. In support of this wave of independence and wanting to ensure that the post-Napoleonic European powers would not return to re-colonize the Western Hemisphere, US President James Monroe established the historic Monroe Doctrine in 1823. At the time, the US did not have the military might to keep Europeans from parts of the Western Hemisphere far from America’s borders. In fact, European nations interfered with Mexico several times after 1823: Spain attempted to re-invade in 1829, France invaded in 1838, Britain threatened to invade in 1861, and France established the Second Mexican Empire in 1862.


US Military Intervention #1: The Boxer Rebellion in China (1900)

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A photograph of an anti-Western “Boxer” rebel in China in 1900, via the National Archives, Washington DC


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After the swift US victory in the Spanish-American War, the US officially became an imperialist power by taking Spain’s island colonies for its own. Less than two years later, the US found itself embroiled in a domestic conflict in China. Since 1839, China had been dominated by Western imperial powers, beginning with Britain forcing open Chinese ports to exploitative trade agreements. This began the Century of Humiliation, in which China was largely at the mercy of the West. In 1898, as the US fought Spain, a growing movement in China sought to push out Western influences. These increasingly-aggressive rebels were known as Boxers for putting on martial arts displays.


In the spring of 1900, the Boxers erupted in widespread violence toward Westerners in major Chinese cities. The Chinese government did little to stop them, and the Boxers killed many Christians and Christian missionaries in Beijing. When the Boxers besieged the foreign legation section of Beijing, seven imperial powers reacted swiftly with military intervention. Along with soldiers from Japan, Russia, France, Italy, Britain, Austria-Hungary, and Germany, US Marines stormed into Beijing and defeated the Boxers. The foreigners were rescued, and China was forced to accept greater imperial domination for the next few decades.


1904: The Roosevelt Corollary (Monroe Doctrine 2.0) 

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US President Theodore “Teddy” Roosevelt, who served from 1901 to 1909, via the National Portrait Gallery, Washington DC


American military performance in the Spanish-American War and the Boxer Rebellion proved that the United States was a force to be reckoned with. A hero from the Spanish-American War, Theodore “Teddy” Roosevelt, became the president in 1901 following the assassination of William McKinley. As President, Roosevelt pursued aggressive foreign policy and became known for the famous quote, “speak softly, and carry a big stick.”


In December 1904, Roosevelt declared that the United States would be the “guarantor of security” in the Western Hemisphere. This served a dual purpose: it kept European powers from interfering in the affairs of nations in Central and South America…but gave the United States the de facto right to do so. Until that point, European powers had threatened military force against nations in Central and South America that did not pay their debts. Now, the US would help ensure that those debts got paid and that pro-American and pro-European governments flourished in the Western Hemisphere.


Intervention #2: Veracruz, Mexico (1914)

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A newspaper headline from 1914 discussing impending US intervention in Mexico, via The Library of Congress, Washington DC


The US fought a war against Mexico in the 1840s, easily defeating its far less industrialized opponent and seizing more than half of its northern territory. Mexico remained in sociopolitical turmoil for many decades afterward, and this turmoil kept tensions with the US elevated. In April 1914, a handful of US sailors were arrested in the port of Tampico, Mexico, when they wandered off course while trying to purchase gasoline. Although the Mexican authorities quickly released the sailors, American pride was gravely insulted. Tensions soared when Mexican leaders refused to give the formal apology that was demanded.


Since the US did not view the current Mexican president, General Victoriano Huerta, as legitimate, the incident gave US President Woodrow Wilson the opportunity to try to remove him. When Huerta refused to give a 21-gun salute to the US flag, Congress approved the use of force against Mexico, and approximately 800 US Marines seized the major port city of Veracruz. The seizure of the city was influenced by the impending arrival of a German ship bringing weapons and ammunition, which Wilson feared could be used by Huerta’s government.


Intervention #3: Haiti (1915)

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US Marines in Haiti in 1915, via The New York Times


Haiti, a small island in the Caribbean known for being the first and only successful formation of a nation due to a slave rebellion, had long been eyed as prime economic territory by the nearby United States. In the early 1900s, Haiti was impoverished and sought international help, including from Germany. The island was also suffering from tremendous political instability and violence, resulting in turmoil. To prevent anarchy (and any potential German incursion, especially since World War I had already begun in Europe), the US Marines invaded the island and seized control in 1915.


Under US intimidation, the Haitian government changed its constitution to allow foreign land ownership, opening up the door to US companies. Policies under the US-dominated Haitian government were initially unpopular and led to peasant uprisings. Although the situation stabilized during most of the 1920s, a new wave of uprisings in 1929 led to the US deciding to leave the island nation. In 1934, the US formally withdrew from Haiti, though the island continued to allow foreign ownership of land.


Intervention #4: Northern Mexico (1916-17)

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US military forces in northern Mexico during the punitive expedition to capture Mexican rebel Pancho Villa, via the United States Army


Despite the US seizure of the port city of Veracruz two years earlier, unrest and violence still plagued Mexico. General Victoriano Huerta, who had provoked US President Woodrow Wilson’s ire, had been replaced later that year by Venustiano Carranza. Unfortunately, Carranza was not liked either, and so Wilson supported a rebel leader named Pancho Villa. When Carranza made enough democratic reforms to make the US happy, support for Villa was withdrawn. In retaliation, Pancho Villa’s men crossed the US border in the spring of 1916 and destroyed the small town of Columbus, New Mexico, after having kidnapped and murdered several Americans on a train in Mexico.


General John J. Pershing, who would soon lead the US forces in France during World War I, crossed into Mexico to capture Pancho Villa. While the thousands of US soldiers were unable to capture the rebel leader, they did clash with forces loyal to President Carranza, who refused to aid the expedition due to its violation of Mexico’s sovereignty. Villa’s forces raided Glenn Springs, Texas in May 1916, prompting the US to send more soldiers to join the expedition.  However, tensions eased after President Carranza apparently acknowledged American anger and US forces left Mexico in February 1917.


Comintern, Domino Theory, & Containment (1919-89) 

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A political cartoon depicting the expansionist and communism-spreading goals of the Soviet Union, via San Diego State University


After World War I and the creation of the League of Nations, which the US decided not to join, violations of other nations’ sovereignty became less socially acceptable. However, World War I helped lead to the rise of communism and the transformation of tsarist Russia into the communist Soviet Union (formally known as the Union of Soviet Socialist Republics, or USSR).  Communism’s goal of eliminating ownership of capital (factories) by individuals and collectivizing all industry and mass production of agriculture under government control directly conflicted with the West’s support of capitalism and free markets.


The Soviet Union openly tried to spread communism to other countries. Comintern, or the Communist International, was the Soviet organization that tried to spread communism between World War I and World War II. After World War II, the rapid rise of Soviet-backed communist governments in nations previously occupied by Nazi Germany and imperialist Japan led to the domino theory, which stated that one nation “falling” to communism would inevitably lead its neighboring nations to do the same. As a result, the US vowed to oppose the spread of communism to new countries as part of a policy of containment during the Cold War (1946-89).


Intervention #5: Iran (1953)

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Soldiers chasing rioters during civil unrest related to the 1953 coup in Iran, via Radio Free Europe


The post-World War II spread of communism occurred hand-in-hand with a drastic reduction in colonialism. Up through World War II, many nations were either directly controlled or heavily influenced by Western imperial powers, such as Great Britain. Iran, a large nation in the Middle East, was subject to such British influence. During World War II, Britain and the Soviet Union invaded Iran to prevent it from potentially becoming an Axis stronghold, as its current leader was somewhat pro-Nazi. Under temporary British control, a new leader was installed, and Iran became a member of the Allied Powers.


After the War, many Iranians disapproved of the Anglo-Iranian Oil Company, which gave Britain tremendous control over Iran’s valuable oil reserves. In 1951, Iran’s popular leader, Mohammad Mossadegh, moved to nationalize the nation’s oil production. The British appealed to the United States for help, and together the two nations engineered a coup to remove Mossadegh from power and return an authoritarian but pro-Western royal leader, the Shah, to active governance.  Although the engineered coup was successful, in 1979, the Iranian Revolution saw a mass uprising against the Shah’s regime and the storming of the US embassy by protesters, resulting in the Iran Hostage Crisis (1979-81).


Intervention #6: Guatemala (1954)

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US President Dwight D. Eisenhower (left) meeting about potential communism in Guatemala in 1954, via the University of Toronto


After World War II, the impoverished nations of Latin America proved to be ripe territory for communist revolutionaries, as low-income peasants had often been mistreated by wealthy landowners and/or Western companies. In 1954, the Second Red Scare was ongoing in the United States, and the country had just finished fighting the Korean War, meaning wariness of communism was at an all-time high. In Guatemala, a country in Central America, new president Jacobo Arbenz was allowing communists seats in his government.


Although the communists were not aggressive, Arbenz further irked the US by proposing land redistribution laws. Much of Guatemala’s best land for agriculture was owned by US fruit companies but remained uncultivated. Arbenz wanted uncultivated land on holdings greater than 670 acres to be redistributed to the people and offered to buy such land from the United Fruit Company. The United Fruit Company, or UFCO, responded by actively portraying Arbenz as a communist, and the US authorized a coup d’état to remove him from power. In May 1954, a CIA-backed rebel attacked the capital, and Arbenz’s government, fearing direct US military intervention, turned against Arbenz and forced him to resign.


Intervention #7: Lebanon (1958) & the Eisenhower Doctrine

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A photograph of US Marines landing on the beach at Beirut, Lebanon in 1958, via the Naval History and Heritage Command


American success in preventing a communist takeover of South Korea in the early 1950s and in deposing alleged communist Jacobo Arbenz in Guatemala in 1954 made active intervention against communism more attractive. Aligned with the policy of containment was the 1957 Eisenhower Doctrine, which affirmed that the US would respond militarily to prevent the rise of international communism in any nation that requested such help. The next year, Lebanon’s president requested US military assistance to stop the rise of his allegedly communist political opponents.


The resulting operation was known as Operation Blue Bat and saw thousands of US troops enter Beirut, Lebanon beginning July 15, 1958. Although the landing of US troops on the beaches of Beirut met with no resistance, the presence of US troops in Lebanon drastically increased tensions between Arab communities and the West. Although Eisenhower tried to link the threat to Lebanon directly to the Soviet Union, it was more likely that his administration feared the rise of Egyptian nationalism next door.


Intervention #8: Bay of Pigs Invasion (1961)

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CIA-backed rebels taken prisoner by Cuban forces in 1961 during the failed Bay of Pigs Invasion, via the University of Miami


Successes in Korea, Guatemala, and Lebanon made it almost inevitable that the US would intervene in Cuba after communist revolutionary Fidel Castro seized power in 1958. Ironically, Castro was initially quite popular with the US media, having overthrown a corrupt and brutal regime under Fulgencio Batista. However, although Batista was unpopular with the people, he was pro-capitalist and sought to turn Havana, Cuba into a haven for American gamblers. Castro angered the US government beginning in 1960 by nationalizing American business property.


Having a communist state so close to America’s shores, especially one that was nationalizing American property, was unacceptable to incoming US President John F. Kennedy. Carrying on a plan devised by predecessor Dwight D. Eisenhower, John F. Kennedy (JFK) had the CIA prepare 1,400 Cuban exiles to return to the island and spark an uprising against Castro. On April 17, 1961, the US dropped the exiles ashore in the ill-fated Bay of Pigs Invasion. The exiles received no air support, and a popular uprising against Castro’s regime did not occur, leaving the exiles to be quickly captured and imprisoned.

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By Owen RustMA Economics in progress w/ MPAOwen is a high school teacher and college adjunct in West Texas. He has an MPA degree from the University of Wyoming and is close to completing a Master’s in Finance and Economics from West Texas A&M. He has taught World History, U.S. History, and freshman and sophomore English at the high school level, and Economics, Government, and Sociology at the college level as a dual-credit instructor and adjunct. His interests include Government and Politics, Economics, and Sociology.