In March 2011, protests break out to demand political change after four decades of repressive rule by the Assad dynasty.
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, the second city.
In 2012 regime forces step up their crackdown, carrying out bloody operations, notably in the central city of Hama, a bastion of opposition to the Assad regime.
In July FSA fighters launch a battle for Damascus. The government keeps 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 same year Iran-backed Lebanese Shiite militant group Hezbollah says 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 kill more than 1,400 people. The regime denies charges that it is responsible.
US president Barack Obama at the last minute pulls back from threatened punitive strikes, instead agreeing a deal with Moscow that is 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.
The strikes benefit Kurdish groups, which since 2013 have run autonomous administrations in Kurdish-majority areas.
Kurds join with Arabs to form the US-backed Syrian Democratic Forces (SDF).
The alliance will go on to oust IS from key areas, including the jihadists' de facto capital Raqa in 2017, and then in 2019, the group's last Syrian holdout in the village of Baghuz 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 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.
In April 2018, the US, with the support of France and Britain, launches retaliatory strikes after an alleged regime chemical attack on the then rebel-held town of Douma, near Damascus.
Turkish 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 follows Washington's announcement that US forces would withdraw from the border areas between Turkey and Syria.
The operation allows Turkey to retake control of a 120-kilometre-long (75-mile-long), 30-kilometre-wide strip of territory along its border with Syria.
Battle for Idlib
In December 2019, the regime launches a deadly offensive in northwestern Syria to retake the country's last major jihadist bastion of Idlib.
Syria's defence ministry announced on January 3,2020 that a convoy of Syrian Kurdish fighters had pulled out of the flashpoint area of Manbij in northern Syria, close to territory controlled by Turkey.
The ministry released video of dozens of vehicles travelling along an unmade road carrying armed fighters, some waving the flags of the Kurdish-led People's Protection Units (YPG) militia and its female counterpart the YPJ. The YPG is the strongest element in the Syrian Defence Forces (SDF), a coalition of militias that the United States has backed in its campaign against Islamic State, helping it capture swathes of north and east Syria.
A blast struck near a US-led coalition patrol in Syria's northern Manbij on January 16 in an attack claimed by Islamic State. The Syrian Observatory for Human Rights war monitoring group said 19 people were killed, including four Americans. An Islamic State-affiliated website, Amaq, said an attacker with an explosive vest had struck a foreign military patrol in a suicide attack.
Syrian Democratic Forces (SDF) fire on Islamic State fighters on February 8, ahead of the February 9 planned assault on the militants' last enclave in the part of Syria where a US-led coalition has been supporting operations against the group.
Dozens of relatives of foreign fighters including Iraqis, Turks, and Russians flee Islamic State's last bastion in eastern Syria on February 12 as the jihadists lose ground to US-backed forces. The Syrian Democratic Forces (SDF), which holds about a quarter of the country, has mounted an attack to seize the enclave with the help of US airstrikes. Roughly 1,500 civilians are evacuated by February 12, the head of media for the Syrian Democratic Forces (SDF) Mustafa Bal said.
Battles slowed this year as a ceasefire held in northwestern Syria and attention turned to containing the coronavirus pandemic. The war has forced more than half the country's pre-war population to flee their homes.