The 1953 coup: For many Iranians, this is the original sin. A joint British-American plot led to the ousting of the country's democratically elected prime minister, Mohammed Mossadegh, in 1953 and the restoration of a monarch, Shah Mohammad Reza Pahlavi, who was pliant to Western interests. Mossadegh had ruffled feathers in London and Washington with his desire to nationalize Iran's oil assets, which were the lifeblood of the mammoth Anglo-Iranian Oil Co. (now better known as BP).
The coup that removed Mossadegh is remembered and referenced widely by Iranians, who point to it as a sign of the West's meddling in Iranian affairs, motivated first and foremost by greed. These anti-imperialist sentiments would underlie the 1979 revolution.
U.S. helps start Iran's nuclear program: In 1957, the United States signed a civil nuclear cooperation deal with the shah of Iran, paving the way for Tehran to build its nuclear program. The initial agreement provided technical assistance and allowed the lease of enriched uranium to Iran.
Iran's capacity slowly grew over the following two decades. In 1975, a West German company began building a nuclear power plant at Bushehr. A year later, the Ford administration even signaled willingness to participate in the shah's plan to construct 23 nuclear power plants in Iran.
The 1979 revolution: Those ambitious nuclear plans didn't come to pass, though, as an anti-monarchist revolution — sparked by nationalists and leftists and later co-opted by Islamists — swept the shah's regime out of power in February 1979. Iran's revolutionary authorities scrapped multibillion-dollar contracts for the construction of a number of nuclear facilities.
Islamist students stormed and occupied the U.S. Embassy in November, leading to a dramatic 444-day-long hostage crisis. Diplomatic relations between the two countries were cut in 1980. The United States would back Iraqi dictator Saddam Hussein in a bloody, eight-year war that kicked off that year with the then-fledgling Islamic republic.
Beirut bombing: In 1983, a suicide bomber targeted a U.S. Marine barracks in the Lebanese capital, leading to the deaths of 241 U.S. military personnel, the deadliest single incident for American troops since the Battle of Iwo Jima. The attack was linked to the Iranian-backed militia Hezbollah. A year later, the Reagan administration listed Iran as a state sponsor of terror.
Iran Air Flight 655: In 1988, an American warship, the USS Vincennes, shot down an Iranian passenger airline, killing all 290 people aboard. The incident followed skirmishes between the U.S. ship and Iranian vessels in the Persian Gulf, and was deemed an accident by the Americans. But many in Iran, particularly hard-liners, were convinced that it was just another sign of the United States' determination to destroy the Islamic republic.
A false dawn: Despite another decade of deepening tensions — including Tehran operatives being linked to terror attacks in Argentina and Saudi Arabia — the 1997 election of reformist Iranian President Mohammad Khatami presented a new opportunity for rapprochement. In an interview with CNN, Khatami called on both countries to bring down the "wall of mistrust." He reiterated Tehran's insistence that it has no desire to produce nuclear weapons. In 2000, U.S. Secretary of State Madeleine Albright publicly acknowledged the harm to Iran's "political development" caused by the Mossadegh coup.
Teamwork: In perhaps the most effective moment of U.S.-Iranian diplomacy since 1979, envoys from both countries worked together at a 2001 conference in Germany to help thrash out a political solution for a new post-Taliban government in Afghanistan. The head Iranian delegate at the meeting was Mohammad Javad Zarif, the country's current foreign minister.
Axis of evil: Things came to a skidding halt in 2003 when President George W. Bush lumped Iran in an "axis of evil" with North Korea and Iraq. The heralding of this fictive geopolitical bloc played a part in the collapse of tentative talks with Khatami's government over Iran's nuclear program.
In 2002, an exiled opposition group revealed the existence of two clandestine Iranian nuclear sites. Khatami acknowledged their existence and invited U.N. inspections, though that did little to ease international concerns. In 2005, the firebrand Mahmoud Ahmadinejad became the Iranian president, and his incendiary rhetoric set the tone in the years to come.
A new hope: In 2013, the more moderate Hassan Rouhani won the presidential election and soon billed his tenure as one that would end Iran's deepening isolation and bring much-need relief to a domestic economy crippled by sanctions. A much-mooted handshake with President Obama did not come to pass at the United Nations in September, but the duo had a historic phone call — the highest level of contact between U.S. and Iranian officials since 1979.
A framework for a deal: After a week of marathon negotiations, Iran and world powers arrived at an agreement to lift international sanctions in exchange for curbs on Iran's nuclear program. A final accord would have to be made by June 30, the deadline to negotiate a final nuclear deal.
[Editor's note: This post was updated to reflect the latest negotiations on an Iran nuclear deal.]