For more than five decades, the U.S. and Iran have negotiated the sensitive terrain of nuclear proliferation.
U.S. President Dwight D. Eisenhower (left) and Shah Mohammad Reza Pahlavi of Iran pose in December 1959 at the Marble Palace in Tehran, Iran.
U.S. President Dwight D. Eisenhower (left) and Shah Mohammad Reza Pahlavi of Iran pose in December 1959 at the Marble Palace in Tehran, Iran. AP
1957: The United States and its then-ally Iran sign a civil nuclear cooperation agreement as part of the U.S. Atoms for Peace program. The agreement allows the lease of several kilograms of enriched uranium to Iran and calls for cooperation on peaceful uses of nuclear energy.
1959: The Shah of Iran orders the establishment of a nuclear research center at Tehran University.
1968: Iran signs the Nuclear Non-Proliferation Treaty on July 1, the day it is opened for signature.
1974: The U.S. and Iran reach a provisional agreement for the U.S. to supply two nuclear power plants and enriched uranium fuel to Iran. In the 1970s, Iran pursues other nuclear power deals with Germany, France and South Africa, among other allies.
1975: The Shah says his country has "no intention of acquiring nuclear weapons but if small states began building them, then Iran might have to reconsider its policy." Later in the '70s, the U.S. obtains intelligence data indicating that the Shah has set up a clandestine nuclear weapons development program.
1978: President Jimmy Carter and the Shah agree on a plan for Iran to purchase between up to eight light water nuclear reactors, pending approval by Congress.
1979: The Islamic Revolution forces the Shah into exile and the taking of U.S. hostages severs U.S.-Iranian relations. During the revolution, an adviser to the Ayatollah Khomeini, who has returned to Iran from exile as a result of the revolution, tells energy specialist Fereydun Fesharaki, "It is your duty to build the atomic bomb for the Islamic Republican Party."
The U.S. severs diplomatic ties with Iran after Iranian militants take more than 50 Americans hostage in 1979. Here, Iranian captors display one of the hostages before the cameras.
The U.S. severs diplomatic ties with Iran after Iranian militants take more than 50 Americans hostage in 1979. Here, Iranian captors display one of the hostages before the cameras. MPI/Getty Images
1981: Reza Amrollahi, the head of the Atomic Energy Organization of Iran, announces that huge uranium deposits have been discovered in four locations in Iran.
1984: Iran opens a nuclear research center at Isfahan with the assistance of China. Reports say that Chinese and Pakistani experts are assisting Iran with obtaining and processing enriched uranium.
1985: The foreign ministers of Iran, Syria and Libya say that their countries should develop nuclear weapons to counter the Israeli nuclear threat.
1985-86: Secret contacts between the United States and Iran lead to a complex deal in which the U.S. supplies conventional weapons to Iran in exchange for Iranian support in Lebanon and the funneling of money to support anti-communist guerrillas in Nicaragua.
Mid-1980s to early 1990s: Iran and North Korea begin cooperating on nuclear issues.
1995: The Clinton administration imposes sanctions prohibiting American companies and their foreign subsidiaries from doing business with Iran, including any financing or development of its oil and gas sector.
President George W. Bush names Iran, along with Iraq and North Korea, the "an axis of evil" during his State of the Union address on Capitol Hill in January 2002.
President George W. Bush names Iran, along with Iraq and North Korea, the "an axis of evil" during his State of the Union address on Capitol Hill in January 2002. Doug Mills/AP
1998: Shortly after taking office, Iran's new reformist president, Mohammad Khatami, calls for a "dialogue among civilizations," raising hopes of a thaw in U.S.-Iranian relations.
2002: President George W. Bush names Iran, along with Iraq and North Korea, as part of "an axis of evil."
2003: Iran begins talks with the International Atomic Energy Agency (IAEA) and British, French and German foreign ministers on nuclear facility inspections. The Khatami government agrees to suspend work on uranium enrichment and allow stepped-up inspections.
2004: Iran agrees — for the time being — to comply with IAEA demands to halt uranium enrichment.
2005: Khatami is succeeded by hard-line conservative Mahmoud Ahmadinejad. Soon after, Iran announces it is resuming work on uranium enrichment.
Stephen Chernin/Getty Images
Members of the United Nations Security Council unanimously approve sanctions against Iran in 2006.
Members of the United Nations Security Council unanimously approve sanctions against Iran in 2006. Stephen Chernin/Getty Images
2006: The U.N. Security Council imposes sanctions on Iran, blocking the import or export of sensitive nuclear material and equipment and freezing the financial assets of persons or entities supporting its proliferation sensitive nuclear activities or the development of nuclear-weapon delivery systems. The sanctions are tightened in subsequent Security Council action in 2007 and 2008.
2007: The U.S. intelligence community releases a National Intelligence Estimate report that claims Iran had suspended its nuclear weapons program in 2003, though its intentions still remain unclear. The NIE says Iran could probably not produce a bomb until the middle of the next decade.
2008: Speculation that Israel could strike at Iran's nuclear program mounts after a large-scale Israeli air force exercise and reports that Israel had made a secret request to the U.S., deflected by the Bush administration, for specialized bunker-busting bombs.
In May 2009, Iran test-fires a Sejil-2 missile, which could reach Israel and American bases in the Persian Gulf.
In May 2009, Iran test-fires a Sejil-2 missile, which could reach Israel and American bases in the Persian Gulf. AFP/Getty Images
2009: In February, international inspectors say that Iran recently understated by one-third how much uranium it has enriched.
In April, the Obama administration says the U.S. would start participating with other major powers in negotiations with Iran over its nuclear program.
In May, Iran test-fires a Sejil-2 missile, which could reach Israel or American bases in the Persian Gulf.
In August, Iran agrees to grant United Nations inspectors greater access to its uranium-enrichment facility at Natanz and the nearly completed heavy water reactor outside Arak. The move comes in anticipation of a report from the International Atomic Energy Agency that is expected to be highly critical of Iran's nuclear program.
Sources: James Martin Center for Nonproliferation Studies at the Monterey Institute of International Studies/NTI, Council on Foreign Relations, Stratfor.com, Globalsecurity.org