FILE - In this May 8, 2018 file photo, President Donald Trump shows a signed Presidential Memorandum after delivering a statement on the Iran nuclear deal from the Diplomatic Reception Room of the White House. The decision Tuesday, Jan 14, 2020, by European nations to trigger a dispute resolution mechanism in the Iran nuclear deal marks the latest step in the unraveling of the accord, which began when President Donald Trump walked away from the agreement and began restoring sanctions on Iran. (AP Photo/Evan Vucci, File)

FILE - In this May 8, 2018 file photo, President Donald Trump shows a signed Presidential Memorandum after delivering a statement on the Iran nuclear deal from the Diplomatic Reception Room of the White House. The decision Tuesday, Jan 14, 2020, by European nations to trigger a dispute resolution mechanism in the Iran nuclear deal marks the latest step in the unraveling of the accord, which began when President Donald Trump walked away from the agreement and began restoring sanctions on Iran. (AP Photo/Evan Vucci, File)

The decision by European nations to trigger a dispute resolution mechanism in the Iran nuclear deal marks the latest step in the unraveling of the accord, which began when President Donald Trump walked away from the agreement and began restoring sanctions on Iran.

The agreement, reached under President Barack Obama, imposed restrictions and stepped-up monitoring of Iran’s nuclear program in exchange for the lifting of international sanctions. Trump and other critics faulted the deal for not addressing Iran’s ballistic missile program or its support for armed groups across the region.

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Even after Trump’s withdrawal, Iran complied with the deal until last summer, when it announced it would begin exceeding limits set by the agreement because it was no longer getting the economic benefits it was promised.

Britain, France, Germany, Russia and China, the other signatories, remain committed to the deal. The European nations have tried but failed to develop a mechanism that would allow them to continue trading with Iran. The U.S. sanctions have devastated Iran’s economy.

On Tuesday, the Europeans said they would trigger the dispute mechanism to try to bring Iran back into compliance with the deal.

Here’s a timeline of major events in the unraveling of the nuclear deal:

July 14, 2015: World powers and Iran announce a long-term, comprehensive nuclear agreement in which Iran curbs its nuclear activities in exchange for the lifting of international sanctions.

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Jan. 16, 2016: The International Atomic Energy Agency acknowledges Iran has met its commitments under the nuclear deal. Meanwhile, the U.S. and Iran make a prisoner swap that frees Washington Post journalist Jason Rezaian and three other Iranian-Americans. The U.S. makes a $400 million cash delivery to Iran the same day. Those funds were related to undelivered military equipment from the shah’s era.

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Nov. 8, 2016: Trump is elected U.S. president after campaigning on promises to scrap the nuclear deal.

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Oct. 13, 2017: Trump announces he will not re-certify the Iran nuclear deal as required, saying the accord “threw Iran’s dictatorship a political and economic lifeline.”

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May 8, 2018: Trump withdraws the U.S. from the nuclear deal. In the coming months, the United States gradually restores economic sanctions on Iran. Britain, France, Germany, Russia and China, the other signatories, say they remain committed to the deal.

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Nov. 5, 2018: U.S. imposes tough sanctions on Iran’s oil industry, the lifeline of its economy, as Secretary of State Mike Pompeo announces a list of 12 demands it must meet for sanctions relief. Iran rejects the wide-ranging demands, which include ending its support for armed groups in the region, withdrawing from the Syrian civil war and halting its ballistic missile program.

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May 8, 2019: Iran vows to enrich its uranium stockpile closer to weapons-grade levels if world powers fail to negotiate new terms for the nuclear deal. The European Union urges Iran to respect the nuclear deal and says it plans to continue trading with the country. Trump says he would like Iran’s leaders to “call me.”

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July 1, 2019: Iran follows through on a threat to exceed the limit set by the nuclear deal on its stockpile of low-enriched uranium, which is used for civilian applications and not for nuclear weapons.

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November 2019: Protests break out across Iran after authorities raise the price of gasoline, the latest of several waves of sporadic, leaderless protests ignited by economic grievances. Amnesty International later says more than 300 people were killed.

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Dec. 27, 2019: A U.S. contractor is killed in a rocket attack on a base in northern Iraq. The U.S. blames the attack on Kataeb Hezbollah, one of several Iran-backed militias operating in Iraq.

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Dec. 29, 2019: U.S. airstrikes hit Kataeb Hezbollah positions in Iraq and Syria, killing at least 25 fighters and bringing vows of revenge. Iraq calls the strikes a “flagrant violation” of its sovereignty.

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Dec. 31, 2019: Hundreds of Iran-backed militiamen and their supporters barge through an outer barrier of the U.S. Embassy in Baghdad and hold two days of violent protests.

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Jan. 3: A U.S. airstrike near Baghdad’s international airport kills Gen. Qassem Soleimani, the leader of Iran’s elite Quds Force and the mastermind of its regional military operations. Iran vows “harsh retaliation.”

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Jan. 5: Iran announces it will no longer abide by the nuclear deal.

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Jan. 8: Iran launches ballistic missiles on two bases in Iraq housing American troops. The missile attack does not hurt anyone, but Iranian forces accidentally shoot down a Ukrainian passenger jet, mistaking it for a U.S. cruise missile. The crash kills all 176 people on board, mainly Iranians.

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Jan. 9: Vice President Mike Pence says Trump will call on European allies to scrap the nuclear deal.

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Jan. 11: After three days of insisting the plane crash was caused by a technical problem, Iranian officials admit to shooting it down. Iranians express shock and outrage, and security forces fire live ammunition and tear gas to disperse protests in Tehran.

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Jan. 14: Britain, France and Germany trigger the agreement’s dispute resolution mechanism, paving the way for possible additional sanctions