The 1953 Iranian coup d'tat, known in Iran as the 28 Mordad coup d'tat (Persian: ), was the overthrow of the democratically elected Prime Minister Mohammad Mosaddegh in favor of strengthening the monarchical rule of the Shah, Mohammad Reza Pahlavi on 19 August 1953. It was orchestrated by the United States (under the name TPAJAX Project or "Operation Ajax") and the United Kingdom (under the name "Operation Boot"). The clergy also played a considerable role.Mosaddegh had sought to audit the documents of the Anglo-Iranian Oil Company (AIOC), a British corporation (now part of BP), in order to verify that AIOC was paying the contracted royalties to Iran, and to limit the company's control over Iranian oil reserves. Upon the AIOC's refusal to co-operate 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 (in power until 1951) opted instead to tighten the economic boycott while using Iranian agents to undermine Mosaddegh's government.:3 Judging Mosaddegh to be unreliable and fearing a Communist takeover in Iran, UK prime minister Winston Churchill and the Eisenhower administration decided in early 1953 to overthrow Iran's government, though the preceding Truman administration had opposed a coup, fearing the precedent that Central Intelligence Agency (CIA) involvement would set.:3 British intelligence officials' conclusions and the UK government's solicitations were instrumental in initiating and planning the coup, despite the fact that the U.S. government in 1952 had been considering unilateral action (without UK support) to assist the Mosaddegh government.Following the coup in 1953, a government under General Fazlollah Zahedi was formed which allowed Mohammad Reza Pahlavi, the last Shah of Iran (Farsi for 'king'), to rule more firmly as monarch. 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.:280 Other Mosaddegh supporters were imprisoned, and several received the death penalty. After the coup, the Shah continued his rule as monarch for the next 26 years 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, including the bribing of Iranian politicians, security and army high-ranking officials, as well as pro-coup propaganda. The CIA is quoted 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".

The Cold War was a period of geopolitical tension between the United States and the Soviet Union and their respective allies, the Western Bloc and the Eastern Bloc, which began following World War II. Historians do not fully agree on its starting and ending points, but the period is generally considered to span the 1947 Truman Doctrine (12 March 1947) to the 1991 dissolution of the Soviet Union (26 December 1991). The term cold war is used because there was no large-scale fighting directly between the two superpowers, but they each supported major regional conflicts known as proxy wars. The conflict was based around the ideological and geopolitical struggle for global influence by these two superpowers, following their temporary alliance and victory against Nazi Germany in 1945. Aside from the nuclear arsenal development and conventional military deployment, the struggle for dominance was expressed via indirect means such as psychological warfare, propaganda campaigns, espionage, far-reaching embargoes, rivalry at sports events and technological competitions such as the Space Race.

The Western Bloc was led by the United States as well as the other First World nations of the Western Bloc that were generally liberal democratic but tied to a network of the authoritarian states, most of which were their former colonies. The Eastern Bloc was led by the Soviet Union and its Communist Party, which had an influence across the Second World and was also tied to a network of authoritarian states. The US government supported anti-communist governments and uprisings across the world, while the Soviet government funded left-wing parties and revolutions around the world. As nearly all the colonial states achieved independence in the period 1945–1960, they became Third World battlefields in the Cold War.

The first phase of the Cold War began shortly after the end of the Second World War in 1945. The United States and its allies created the NATO military alliance in 1949 in the apprehension of a Soviet attack and termed their global policy against Soviet influence containment. The Soviet Union formed the Warsaw Pact in 1955 in response to NATO. Major crises of this phase included the 1948–1949 Berlin Blockade, the 1927–1949 Chinese Civil War, the 1950–1953 Korean War, the 1956 Hungarian Revolution, the 1956 Suez Crisis, the Berlin Crisis of 1961 and the 1962 Cuban Missile Crisis. The US and the USSR competed for influence in Latin America, the Middle East, and the decolonizing states of Africa, Asia, and Oceania.

Following the Cuban Missile Crisis, a new phase began that saw the Sino-Soviet split between China and the Soviet Union complicate relations within the Communist sphere, while France, a Western Bloc state, began to demand greater autonomy of action. The USSR invaded Czechoslovakia to suppress the 1968 Prague Spring, while the US experienced internal turmoil from the civil rights movement and opposition to the Vietnam War. In the 1960s–1970s, an international peace movement took root among citizens around the world. Movements against nuclear weapons testing and for nuclear disarmament took place, with large anti-war protests. By the 1970s, both sides had started making allowances for peace and security, ushering in a period of détente that saw the Strategic Arms Limitation Talks and the US opening relations with the People's Republic of China as a strategic counterweight to the USSR. A number of self-proclaimed Marxist regimes were formed in the second half of the 1970s in the Third World, including Angola, Mozambique, Ethiopia, Cambodia, Afghanistan and Nicaragua.

Détente collapsed at the end of the decade with the beginning of the Soviet–Afghan War in 1979. The early 1980s was another period of elevated tension. The United States increased diplomatic, military, and economic pressures on the Soviet Union, at a time when it was already suffering from economic stagnation. In the mid-1980s, the new Soviet leader Mikhail Gorbachev introduced the liberalizing reforms of glasnost ("openness", c. 1985) and perestroika ("reorganization", 1987) and ended Soviet involvement in Afghanistan in 1989. Pressures for national sovereignty grew stronger in Eastern Europe, and Gorbachev refused to militarily support their governments any longer.

In 1989, the fall of the Iron Curtain after the Pan-European Picnic and a peaceful wave of revolutions (with the exception of Romania and Afghanistan) overthrew almost all communist governments of the Eastern Bloc. The Communist Party of the Soviet Union itself lost control in the Soviet Union and was banned following an abortive coup attempt in August 1991. This in turn led to the formal dissolution of the USSR in December 1991, the declaration of independence of its constituent republics and the collapse of communist governments across much of Africa and Asia. The United States was left as the world's sole superpower.

The Cold War and its events have left a significant legacy. It is often referred to in popular culture, especially with themes of espionage and the threat of nuclear warfare. For subsequent history see International relations since 1989.