1953 Iranian coup d'état

On 19 August 1953, Prime Minister of Iran Mohammad Mosaddegh was overthrown in a coup d'état that strengthened the rule of Mohammad Reza Pahlavi, the Shah of Iran. It was instigated by the United Kingdom (MI6), under the name Operation Boot and the United States (CIA), under the name TP-AJAX Project or Operation Ajax. A key motive was to protect British oil interests in Iran after Mosaddegh nationalized the country's oil industry.

Mosaddegh had sought to audit the documents of the Anglo-Iranian Oil Company (AIOC), a British corporation (now part of BP), to verify that AIOC was paying the contracted royalties to Iran, and to limit their control over Iranian oil reserves. Upon the AIOC's refusal to cooperate with the Iranian government, the parliament (Majlis) voted to nationalize Iran's oil industry and to expel foreign corporate representatives from the country. After this vote, Britain instigated a worldwide boycott of Iranian oil to pressure Iran economically. Initially, Britain mobilized its military to seize control of the British-built Abadan oil refinery, then the world's largest, but Prime Minister Clement Attlee opted instead to tighten the economic boycott while using agents to undermine Mosaddegh's government. Judging Mosaddegh to be unamenable and fearing the growing influence of the communist Tudeh, Attlee's succeeding UK prime minister Winston Churchill decided in early 1953 to solicit the Eisenhower administration and overthrow Iran's government. The preceding Truman administration had opposed a coup, fearing the precedent that Central Intelligence Agency involvement would set, and the U.S. government had been considering unilateral action (without UK support) to assist the Mosaddegh government as late as 1952. British intelligence and the UK government's solicitations to the US were instrumental in initiating and planning the coup. In the week before the coup, Mosaddegh consolidated power through a controversial referendum to dissolve parliament.

The events of the coup unfolded between 15 and 19 of August, after months of planning by the United States' CIA, and United Kingdom's MI6. On 15 August, an officer of the Imperial Guard of the Shah (Persian for 'king') was dispatched to Tehran to deliver the Shah's dismissal decree to Mosaddegh, a move that was legally questionable under the 1906–1907 Iranian Constitution. Upon arrival, the officer was arrested by Mosaddegh's supporters, and the Shah, Mohammed Reza Pahlavi fled to Italy shortly afterward. After the Shah left, a wave of protests organized by the CIA failed to overthrow Mosaddegh. Although the initial attempt failed, the CIA continued coordinating with royalist networks, clerical figures, and elements of the military. On 19 August, demonstrators and military units backed by the CIA gained control of key institutions in Tehran and seized the government, leading to Mosaddegh's overthrow on 19 August, allowing the Shah to return to Iran on 22 August.

Following the coup, a government under General Fazlollah Zahedi, who led the military units in support of the coup, was formed, which allowed the Shah of Iran , to rule more firmly as monarch. After his return to Iran, he relied heavily on United States support to hold on to power. According to the CIA's declassified documents and records, some of the most feared mobsters in Tehran were hired by the CIA to stage pro-shah riots on 19 August. Other men paid by the CIA were brought into Tehran in buses and trucks and took over the streets of the city. Between 200 and 300 people were killed because of the conflict. Mosaddegh was arrested, tried and convicted of treason by the Shah's military court. On 21 December 1953, he was sentenced to three years in jail, then placed under house arrest for the remainder of his life. Other Mosaddegh supporters were imprisoned, and several received the death penalty. The coup strengthened the Shah's authority, and he continued to rule Iran for the next 26 years as an authoritarian, pro-Western monarch, until he was overthrown in the Iranian Revolution in 1979.

In August 2013, the U.S. government formally acknowledged the U.S. role in the coup by releasing a bulk of previously classified government documents that show it was in charge of both the planning and the execution of the coup. According to American journalist Stephen Kinzer, the operation included false flag attacks, paid protesters, provocations, the bribing of Iranian politicians and high-ranking security and army officials, as well as pro-coup propaganda. The CIA is quoted as acknowledging the coup was carried out "under CIA direction" and "as an act of U.S. foreign policy, conceived and approved at the highest levels of government". In 2023, the CIA took credit for the coup, this confirmed what many historians had already concluded before, though because portions of the agency's records were destroyed, or remained classified for years, some historians had initially argued, on the basis of incomplete evidence, that Iranian domestic actors played the primary role in the coup, with the U.S. and Britain serving mainly in a supporting capacity.