Summer of 2014: The U.S. administration reveals that several dozen special operations troops had been on the ground in Syria briefly in an effort to rescue foreign hostages taken by the Islamic State group, but did not find them.
Sept. 22, 2014: Obama launches a U.S. air campaign against the Islamic State in Syria, one month after launching airstrikes in neighbouring Iraq. To date, the U.S.-led coalition has launched airstrikes on at least 17,000 locations in Syria since the start of the operation.
Late 2015: The first American ground troops enter Syria — initially 50, growing to the current official total of about 2,000. They recruit, organize and advise thousands of Syrian Kurdish and Arab fighters, dubbed the Syrian Democratic Forces, and push IS out of most of its strongholds.
November 24, 2016: Senior Chief Petty Officer Scott Cooper Dayton, 42, of Woodbridge, Virginia, is killed in an improvised explosive device blast near the northern Syrian town of Ayn Issa, becoming the first American casualty in combat in the fight against IS in Syria.
April 4, 2017: More than 90 people are killed in a suspected nerve gas attack on the town of Khan Sheikhoun in the rebel-held Idlib province. Moscow and Damascus deny responsibility.
April 5, 2017: Trump says Assad’s government has “crossed a lot of lines” with the suspected chemical attack in Syria and a day later, the U.S. fires 59 cruise missiles into Syria in retaliation — the first direct American assault on the Syrian government.
March 30, 2018: U.S. Master Sgt. Jonathan J. Dunbar is killed by a roadside bomb attack in Syria alongside a British serviceman.
April 7, 2018: Syrian activists, rescuers and medics say a poison gas attack on the rebel-held town of Douma near the capital has killed at least 40 people. The Syrian government and Russia reject the allegations, saying the purported evidence of the chemical weapons attack was fabricated.
April 8, 2018: Trump calls Assad an “animal” and says there would be a “big price to pay” for resorting to outlawed weapons of mass destruction.
April 15, 2018: The United State, Britain and France launch missile attacks on the Syrian capital Damascus and the central province of Homs in retaliation for the Douma attack. Syria says its air defences intercepted most of the missiles fired.
December 19, 2018: Trump announces on Twitter his intention to withdraw troops from Syria, adding in a video posted to Twitter, “now it’s time for our troops to come back home.” The withdrawal is initially expected to be carried out within weeks.
Dec. 21, 2018: Defence Secretary Jim Mattis and Brett McGurk, the administration’s special envoy to the global anti-IS coalition, resign in protest.
Jan. 6, 2019: U.S. national security adviser John Bolton says during a visit to Israel that U.S. troops will not leave northeastern Syria until IS militants are defeated and American-allied Kurdish fighters are protected. The comments appear to put the brakes on the withdrawal abruptly announced by Trump.
Jan. 8, 2019: Turkish President Recep Tayyip Erdogan accuses the U.S. national security adviser of making “a very serious mistake” by demanding that Ankara guarantee the safety of Kurdish fighters in northeastern Syria before the U.S. withdraws its troops.
Jan. 11, 2019: A U.S. defence official in Washington says some military cargo has been pulled out of Syria, marking the beginning of the withdrawal process.