Syria's war since 2011 has involved a host of regional and international players, forced millions of people from their homes and left more than 380,000 people dead.
Here is a summary of the main events in the nine-year conflict:
Revolt to repression
In March 2011, protests break out calling for political change after four decades of repressive rule by the Assad dynasty, Bashar having succeeded his father Hafez in 2000.
President Bashar al-Assad's regime cracks down on demonstrations, but rallies continue.
In July, an army colonel, who has defected from the military, sets up the Turkey-based opposition Free Syrian Army (FSA).
An armed rebellion erupts with support from Western and Arab countries. The rebels seize key territory, including large swathes of third city Homs and a chunk of Aleppo, Syria's second city.
In 2012, the regime carries out bloody operations, notably in the central city of Hama, a bastion of opposition to the Assad regime.
FSA fighters in July launch a battle for Damascus. The government retains control of the capital, but rebels seize parts of the suburbs.
From 2013, regime helicopters and planes unleash air strikes, some of them using barrel bombs, on rebel zones, according to the Syrian Observatory for Human Rights.
The Iran-backed Lebanese Shiite militant group Hezbollah says in 2013 it has deployed fighters to back Syrian government forces.
Iran also boosts its support for Assad.
US steps back
On August 21, 2013, a chemical attack on two rebel-held areas near Damascus reportedly kills more than 1,400 people. The regime denies responsibility.
US president Barack Obama pulls back from threatened punitive strikes, instead agreeing a deal with Moscow meant to dismantle Syria's chemical weapons arsenal.
Islamic State group
In June 2014, the jihadist Islamic State group (IS) proclaims a "caliphate" over territory it has seized in Syria and Iraq.
In September, a US-led coalition launches air strikes against IS in Syria.
Kurdish groups, which since 2013 have set up autonomous administrations in Kurdish-majority areas, join with Arabs to form the US-backed Syrian Democratic Forces (SDF).
The alliance ousts IS from key areas, including its de facto capital Raqa, in 2017, and then in 2019, the group's last Syrian holdout in the village of Baghouz near the border with Iraq.
Russia rescues Assad
In September 2015, Syria's main ally Russia launches air strikes in support of Assad's beleaguered troops, a turning point in the war.
In a string of deadly campaigns, the regime retakes key rebel bastions, from Aleppo in 2016 to Eastern Ghouta on the outskirts of the capital in 2018.
In April 2017, a sarin gas attack on the rebel-held town of Khan Sheikhun kills more than 80 people.
US President Donald Trump unleashes missile strikes against the regime's Shayrat airbase, from where the gas attack was allegedly launched.
In April 2018, the US, France and Britain launch retaliatory strikes after an alleged regime chemical attack on the then rebel-held town of Douma, near Damascus.
Turkey offensive against Kurds
On October 9, 2019, Ankara launches an offensive targeting Kurdish forces in Syria, whom it brands "terrorists" linked to Kurdish insurgents in Turkey.
The operation allows Turkey to take control of a 120-kilometre-long (75-mile-long), 30-kilometre-wide strip of territory along the border.
Battle for Idlib
In December 2019, the regime launches a deadly offensive to retake Idlib, the last major jihadist bastion in Syria.
A ceasefire is reached in March 2020 after months of bombardment and fighting.