BEIRUT (AFP) - US missiles targeted Syrian forces Friday (April 7) in response to a suspected chemical attack that killed up to 86 people earlier this week.
It was the first direct US strike against the government of President Bashar al-Assad in Syria's devastating six-year war.
Here is a look at Washington's previous involvement in the conflict.
Pressure on Assad
April 29, 2011: Responding to a bloody regime crackdown against protests, Washington slaps sanctions and asset freezes on Syrian officials including President Bashar al-Assad's powerful brother, Maher.
May 19: A day after ordering the first direct sanctions against Assad himself, US president Barack Obama calls on the Syrian leader to lead a political transition or step aside.
July 8: The US ambassador in Damascus, Robert Ford, challenges Assad by visiting Hama, a central city besieged by the army and scene of a massive demonstration against the regime.
Aug 18: Obama and Western allies for the first time call explicitly on Assad to stand down.
Oct 24: The United States announces that Ford has left Syria for security reasons. Damascus recalls its ambassador from Washington.
Obama ignores 'red line'
Sept 14, 2013: Following an August 21 chemical weapons attack attributed to Assad's regime, Russia and the United States agree to dismantle Syria's chemical weapons arsenal, averting the threat of a punitive US strike.
Obama had vowed to act if Syria crossed the "red line" of chemical weapons use. His failure to follow through upsets allies such as France and Saudi Arabia.
Strikes against ISIS
Sept 23, 2014: The United States and Arab allies launch air strikes in Syria against the Islamic State in Iraq and Syria (ISIS) group, which has emerged as the strongest group fighting the regime. The strikes expand a US-led campaign against the extremists in neighbouring Iraq.
Moscow enters the fray
Sept 30, 2015: Regime backer Russia launches air strikes in support of Assad. Moscow says it is targeting "terrorist groups" including ISIS, but most of the strikes target non-extremist rebels.
The regime, on the back foot since March 2015, begins to retake territory.
In 2016, American and Russian-brokered ceasefires quickly break down, but after an all-out assault by Russian and Syrian forces ousts rebels from second city Aleppo, a truce negotiated without the US takes effect on December 30.
Trump takes office
Nov 15, 2016: Assad declares that US president-elect Donald Trump will be "a natural ally" if he decides to fight terrorism in Syria.
Syrian officials apply the term "terrorist" to all groups fighting the regime, including the US-backed Syrian Democratic Forces.
March 30, 2017: US Secretary of State Rex Tillerson says Assad's fate "will be decided by the Syrian people." US ambassador to the UN Nikki Haley adds that "our priority is no longer to sit and focus on getting Assad out." .
First US strike
April 4, 2017: Trump's tone hardens after a suspected chemical attack kills as many as 86 people in Idlib province.
"My attitude towards Syria and Assad has changed very much ... You're now talking about a whole different level," he says two days later.
The following morning, a pre-dawn wave of 59 US cruise missiles rips up Shayrat airfield in central Syria, the suspected launch site of the Idlib attack.