The 1954 Guatemalan coup d'tat, code-named Operation PBSuccess, was a covert operation carried out by the U.S. Central Intelligence Agency (CIA) that deposed the democratically elected Guatemalan President Jacobo rbenz and ended the Guatemalan Revolution of 19441954. It installed the military dictatorship of Carlos Castillo Armas, the first in a series of U.S.-backed authoritarian rulers in Guatemala.

The Guatemalan Revolution began in 1944, after a popular uprising toppled the military dictatorship of Jorge Ubico. Juan Jos Arvalo was elected president in Guatemala's first democratic election. He introduced a minimum wage and near-universal suffrage, and turned Guatemala into a democracy. Arvalo was succeeded in 1951 by rbenz, who instituted land reforms which granted property to landless peasants. The Guatemalan Revolution was disliked by the United States federal government, which was predisposed during the Cold War to see it as communist. This perception grew after rbenz had been elected and formally legalized the communist Guatemalan Party of Labour. The United Fruit Company (UFC), whose highly profitable business had been affected by the end to exploitative labor practices in Guatemala, engaged in an influential lobbying campaign to persuade the U.S. to overthrow the Guatemalan government. U.S. President Harry Truman authorized Operation PBFortune to topple rbenz in 1952; although the operation was quickly aborted it was a precursor to PBSuccess.

Dwight D. Eisenhower was elected U.S. president in 1952, promising to take a harder line against communism; the links that his staff members John Foster Dulles and Allen Dulles had to the UFC also predisposed them to act against the Guatemalan government. Additionally, the U.S. federal government drew exaggerated conclusions about the extent of communist influence among rbenz's advisers. Eisenhower authorized the CIA to carry out Operation PBSuccess in August 1953. The CIA armed, funded, and trained a force of 480 men led by Carlos Castillo Armas. The coup was preceded by U.S. efforts to criticize and isolate Guatemala internationally. Castillo Armas' force invaded Guatemala on 18 June 1954, backed by a heavy campaign of psychological warfare. This included a radio station which broadcast anti-government propaganda and a version of military events favorable to the rebellion, claiming to be genuine news, as well as air bombings of Guatemala City and a naval blockade. The invasion force fared poorly militarily, and most of its offensives were defeated. However, psychological warfare and the fear of a U.S. invasion intimidated the Guatemalan army, which eventually refused to fight. rbenz briefly and unsuccessfully attempted to arm civilians to resist the invasion, before resigning on 27 June. Castillo Armas became president ten days later, following negotiations in San Salvador.

Described as the definitive deathblow to democracy in Guatemala, the coup was widely criticized internationally, and strengthened the long-lasting anti-U.S. sentiment in Latin America. Attempting to justify the coup, the CIA launched Operation PBHistory, which sought evidence of Soviet influence in Guatemala among documents from the rbenz era; the effort was a failure. Castillo Armas quickly assumed dictatorial powers, banning opposition parties, imprisoning and torturing political opponents, and reversing the social reforms of the revolution. Nearly four decades of civil war followed, as leftist guerrillas fought the series of U.S.-backed authoritarian regimes whose brutalities include a genocide of the Maya peoples.

Carlos Castillo Armas (locally ['kaɾlos kas'tiʝo 'aɾmas]; 4 November 1914 – 26 July 1957) was a Guatemalan military officer and politician who was the 28th president of Guatemala, serving from 1954 to 1957 after taking power in a coup d'état. A member of the right-wing National Liberation Movement (MLN) party, his authoritarian government was closely allied with the United States.

Born to a planter, out of wedlock, Castillo Armas was educated at Guatemala's military academy. A protégé of Colonel Francisco Javier Arana, he joined Arana's forces during the 1944 uprising against President Federico Ponce Vaides. This began the Guatemalan Revolution and the introduction of representative democracy to the country. Castillo Armas joined the General Staff and became director of the military academy. Arana and Castillo Armas opposed the newly elected government of Juan José Arévalo; after Arana's failed 1949 coup, Castillo Armas went into exile in Honduras. Seeking support for another revolt, he came to the attention of the US Central Intelligence Agency (CIA). In 1950 he launched a failed assault on Guatemala City, before escaping back to Honduras. Influenced by lobbying by the United Fruit Company and Cold War fears of communism, in 1952 the US government of President Harry Truman authorized Operation PBFortune, a plot to overthrow Arévalo's successor, President Jacobo Árbenz. Castillo Armas was to lead the coup, but the plan was abandoned before being revived in a new form by US President Dwight D. Eisenhower in 1953.

In June 1954, Castillo Armas led 480 CIA-trained soldiers into Guatemala, backed by US-supplied aircraft. Despite initial setbacks to the rebel forces, US support for the rebels made the Guatemalan army reluctant to fight, and Árbenz resigned on 27 June. A series of military juntas briefly held power during negotiations that ended with Castillo Armas assuming the presidency on 7 July. Castillo Armas consolidated his power in an October 1954 election, in which he was the only candidate; the MLN, which he led, was the only party allowed to contest the congressional elections. Árbenz's popular agricultural reform was largely rolled back, with land confiscated from small farmers and returned to large landowners. Castillo Armas cracked down on unions and peasant organizations, arresting and killing thousands. He created a National Committee of Defense Against Communism, which investigated over 70,000 people and added 10 percent of the population to a list of suspected communists.

Castillo Armas faced significant internal resistance, which was blamed on communist agitation. The government, plagued by corruption and soaring debt, became dependent on aid from the US. In 1957 Castillo Armas was assassinated by a presidential guard with leftist sympathies. He was the first of a series of authoritarian rulers in Guatemala who were close allies of the US. His reversal of the reforms of his predecessors sparked a series of leftist insurgencies in the country after his death, culminating in the Guatemalan Civil War of 1960 to 1996.