Why have Iran and the United States been enemies for decades?

The short answer

Iran and the United States became adversaries through successive political choices and crises. The US-backed overthrow of Prime Minister Mohammad Mosaddegh in 1953 and the subsequent partnership with the Shah left lasting distrust among opponents of the monarchy. The 1979 revolution and embassy hostage crisis broke that partnership; war, sanctions and competing regional ambitions later made reconciliation harder.^[2][7]

“Enemies” describes the relationship between governments. It does not mean that Iranians and Americans share a single view of one another, or that confrontation has excluded negotiation.

Before 1953: hostility was not the starting point

American diplomatic relations with Iran, then commonly called Persia in foreign correspondence, were established in 1883. The relationship therefore long predates the Islamic Republic. Its later rupture was a historical change, not the continuation of an ancient rivalry.^[1]

Iran’s position between competing powers became especially important during the Second World War and the early Cold War. British and Soviet troops occupied Iran in 1941; US forces later joined the wartime supply effort. Soviet support for separatist movements in northern Iran after the war sharpened American concerns about Soviet expansion. That background helps explain Washington’s anxieties in the early 1950s, but it does not establish that a communist takeover was imminent.^[3]

What happened in the 1953 coup?

Mosaddegh, a nationalist prime minister with parliamentary support, championed the nationalization of Iran’s British-controlled oil industry in 1951. For his supporters, control of oil revenues was a question of sovereignty. Britain sought to reverse the loss of its position. A dispute over oil became entangled with a struggle over who would govern Iran.^[3]

On 19 August 1953, a coup backed by the CIA and Britain’s intelligence service removed Mosaddegh. General Fazlollah Zahedi became prime minister, and Mohammad Reza Pahlavi, the Shah, returned after briefly leaving Iran. Iranian officers, political networks and street mobilization were part of the operation. Describing the coup as either wholly foreign or wholly domestic misses this interaction.^[2]

The foreign intervention is documented; its motives and the relative contribution of different participants remain subjects of historical debate. Cold War explanations emphasize US fears about the Soviet-aligned Tudeh Party. Oil-centered explanations emphasize control of a valuable industry. Mosaddegh was not himself a communist. In a 2019 study of contemporary US assessments, historian Mark Gasiorowski argues that the available evidence did not show an immediate communist threat when American leaders decided to overthrow him.^[3]

The coup became a powerful reference point for later opponents of US influence. But twenty-six years separated it from the revolution. What happened during those years also needs explaining.

The Shah’s alliance with Washington carried a political cost

After 1953, US–Iran relations developed around the monarchy. The partnership combined security interests with the Shah’s own ambition to make Iran a major regional power. A July 1972 memorandum from Henry Kissinger records President Richard Nixon’s willingness to supply advanced aircraft and other military equipment, leaving purchasing decisions largely to Iran. The Shah was an active partner with his own priorities, even as he depended heavily on American equipment.^[4]

Economic and social development accompanied concentrated political power. In January 1973, the US embassy described a country undergoing rapid growth while its parliament, press and political parties remained closely controlled. It also acknowledged the fear generated by SAVAK, the Shah’s security organization. The same assessment nevertheless treated the monarchy as a dependable source of regional stability.^[5]

This is a revealing tension in the alliance. American officials could recognize authoritarian rule while continuing to value the ruler as a security partner. For opponents who associated the monarchy with foreign backing, the relationship gave domestic grievances an international dimension. Development did not settle questions of political participation or legitimacy.

Why the 1979 revolution changed the relationship

The movement that overthrew the Shah was not politically uniform. Religious activists, nationalists and leftists opposed the monarchy for different reasons and disagreed about what should replace it. Ayatollah Ruhollah Khomeini became its dominant leader, but the final distribution of power was not settled simply by the Shah’s departure.^[6]

The revolution ended the old alliance. Yet even then, a complete diplomatic break was not the only course being considered. The provisional government of Mehdi Bazargan sought working relations with Washington. Khomeini and competing revolutionary institutions had much greater power, and opposition to American influence became bound up with the struggle to define the new state.^[7]

Treating the revolution as a unanimous vote for permanent hostility erases those differences. It also obscures the decisions that followed: the embassy seizure was a distinct turning point, not simply another name for the revolution.

The hostage crisis turned rupture into sustained confrontation

On 22 October 1979, the United States admitted the deposed Shah for medical treatment. Revolutionary opponents feared another foreign-backed restoration. On 4 November, Iranian students seized the US embassy in Tehran. Khomeini supported the takeover. Political scientist Mohsen Milani interprets the prolonged crisis as a means by which Khomeini’s camp weakened its domestic rivals as well as confronted Washington.^[7]

For Americans, the captivity of diplomatic personnel became a defining experience of the new Iranian government. Fifty-two Americans remained hostage for 444 days. Negotiations, economic pressure and a failed US rescue operation in April 1980 made the crisis the central problem of Jimmy Carter’s final year in office. The US State Department’s own history describes its damaging effect on his administration.^[8][20]

Washington severed diplomatic relations on 7 April 1980. The remaining hostages were released on 20 January 1981, but that did not restore the relationship. Fear of foreign intervention and anger over hostage-taking had become separate, deeply felt reasons for mistrust.^[1]

The Iran–Iraq War added another set of grievances

Saddam Hussein’s Iraq invaded Iran in September 1980. As the war continued, the Reagan administration moved toward supporting Iraq to prevent an Iranian victory. Declassified records show US officials knew Iraq was using chemical weapons. Washington publicly condemned that use in 1984 while continuing efforts to strengthen ties with Baghdad. The record therefore supports a more precise account than either “the US knew nothing” or “the US never objected.”^[9]

From Iran’s perspective, the wartime relationship between Washington and Baghdad gave concrete weight to fears of hostile encirclement. That helps explain a security outlook; it does not establish that Washington ordered Iraq’s invasion. The sources cited here do not demonstrate that claim.

Hostility also coexisted with covert bargaining. In 1985–1986, US officials arranged arms transfers to Iran in an effort linked to securing the release of American hostages in Lebanon. The Iran–Contra affair showed that publicly antagonistic governments could still pursue limited transactions when their interests overlapped.^[10]

In July 1988, the US warship Vincennes shot down Iran Air Flight 655 over the Gulf, killing all 290 people aboard. American officials said the civilian airliner had been mistaken for a military aircraft. The deaths added a direct human loss to the history of confrontation.^[20]

Why sanctions became central

Sanctions are restrictions on economic dealings, assets or access to finance. US measures against Iran accumulated over time rather than beginning with the nuclear dispute. They included the freezing of Iranian government property in November 1979 and broader trade and investment restrictions in the 1990s. Later measures addressed nuclear activities, terrorism-related designations and other policy concerns under different authorities.^[11]

That layering matters. A nuclear agreement could remove some restrictions without restoring ordinary economic relations. In November 2018, the US Treasury presented renewed sanctions as a way to restrict the Iranian government’s resources and pressure it to change its behavior. That is the administration’s stated rationale, not proof that the policy achieved its objectives.^[16]

The effects also reach beyond officials. US rules provide humanitarian authorizations, but permitted trade can still face practical obstacles. In a February 2023 communication, UN independent experts raised concerns about access to medicines and businesses avoiding transactions because of sanctions risks. Their letter reported allegations and sought a response; it was not a court judgment. Sanctions debates must distinguish legal exemptions from what patients and suppliers can actually obtain.^[11][12]

What role does the nuclear issue play?

The nuclear dispute added a question with potentially enormous consequences: could Iran’s program provide a path to nuclear weapons? Uranium enrichment increases the proportion of a particular isotope, uranium-235. Enriched uranium can fuel reactors; much higher enrichment can provide material for a weapon. Enrichment, weapons-related research and possession of a functioning bomb are different things.

Iran has maintained that its program is peaceful. That official position must be distinguished from the findings of international inspectors. In its December 2015 assessment, the International Atomic Energy Agency (IAEA) concluded that coordinated work relevant to a nuclear explosive device had occurred before the end of 2003, with some activity afterward. It assessed that the work had not progressed beyond feasibility studies, scientific research and acquiring technical capabilities, and reported no credible indications of such activity after 2009. Those were findings about the evidence available in 2015, not a guarantee about later developments.^[13]

The JCPOA made a limited bargain possible

On 14 July 2015, Iran and six powers—the United States, Britain, France, Germany, Russia and China—with the European Union reached the Joint Comprehensive Plan of Action, or JCPOA. It exchanged restrictions on Iran’s nuclear program and expanded monitoring for nuclear-related sanctions relief.

Among its provisions were a fifteen-year enrichment ceiling of 3.67 percent and limits on the enriched-uranium stockpile. Other restrictions had different durations. The agreement addressed a defined nuclear problem; it did not resolve the regional conflicts or transform the two countries into allies.^[14]

President Donald Trump withdrew the United States on 8 May 2018, and his administration restored sanctions. European governments opposed the decision. Their declaration the following day cited repeated IAEA confirmation that Iran was implementing its nuclear commitments. The distinction matters: the US decision to leave was not an IAEA finding that Iran had already abandoned the deal.^[15][16]

From 2019, Iran progressively exceeded the agreement’s limits and later curtailed monitoring. The IAEA documented those changes. The order of events helps explain the breakdown, without making either side’s later choices automatic or removing its responsibility for them.^[17]

Regional competition made the dispute larger than a nuclear deal

Iran developed ties with Hezbollah in Lebanon, armed groups in Iraq, Palestinian organizations and Yemen’s Houthis. These relationships differed in origin and strength. The Islamic Revolutionary Guard Corps’ Quds Force played an important role in supporting partners abroad. US forces and regional allies faced threats from parts of this network, giving Washington concerns that a nuclear agreement alone could not address.^[18]

Analysts differ over how to weigh Iran’s search for influence against its efforts to deter threats to its own government. In a US Institute of Peace report, Barbara Slavin emphasized defensive motives while also noting the costs imposed on others and the autonomy of Iranian partners. Calling a group a “proxy” should not substitute for evidence about who decided on a particular attack.^[19]

The confrontation sometimes became direct. In January 2020, a US strike killed Quds Force commander Qassem Soleimani in Baghdad. Iran retaliated with missile strikes on bases housing US forces in Iraq. Such exchanges created new grievances alongside the older ones.^[20]

Why the conflict still matters

In June 2025, Israeli and US attacks hit Iranian nuclear facilities. The IAEA subsequently reported severe disruption to inspection and monitoring. Military attacks and reduced access therefore created problems not only for security but also for establishing what had happened to nuclear material and facilities.^[17]

A much wider US–Israeli campaign began on 28 February 2026. Iran retaliated against Israel and US facilities in the region. This marked a major escalation beyond sanctions and indirect competition.^[20]

Recent-events cutoff: 11 September 2026. Associated Press reporting on that date described continuing fighting and disruption around the Strait of Hormuz despite increased shipping through it. A passage connecting the Gulf to the open sea had become a point where military confrontation affected trade and energy supplies far beyond the region.^[21]

The historical connection is not a single chain of unavoidable consequences. The coup damaged trust; the Shah’s alliance tied the United States to a contested political order; the revolution and hostage crisis broke relations; subsequent war and policy choices repeatedly renewed the conflict. Diplomacy, including the JCPOA, shows that particular disputes can still be negotiated. It also shows how vulnerable a limited agreement remains when the wider confrontation continues.