Syria: The story of the conflict
More than 250,000 Syrians have lost their lives in four-and-a-half years of armed conflict, which began with anti-government protests before escalating into a full-scale civil war. More than 11 million others have been forced from their homes as forces loyal to President Bashar al-Assad and those opposed to his rule battle each other - as well as jihadist militants from so-called Islamic State. This is the story of the civil war so far, in eight short chapters.
1. Uprising turns violent
Pro-democracy protests erupted in March 2011 in the southern city of Deraa after the arrest and torture of some teenagers who painted revolutionary slogans on a school wall. After security forces opened fire on demonstrators, killing several, more took to the streets.
The unrest triggered nationwide protests demanding President Assad's resignation. The government's use of force to crush the dissent merely hardened the protesters' resolve. By July 2011, hundreds of thousands were taking to the streets across the country.
2. Descent into civil war
Violence escalated and the country descended into civil war as rebel brigades were formed to battle government forces for control of cities, towns and the countryside. Fighting reached the capital Damascus and second city of Aleppo in 2012.
By June 2013, the UN said 90,000 people had been killed in the conflict. By August 2015, that figure had climbed to 250,000, according to activists and the UN.
3. War crimes
A UN commission of inquiry has evidence that all parties to the conflict have committed war crimes - including murder, torture, rape and enforced disappearances. They have also been accused of using civilian suffering - such as blocking access to food, water and health services through sieges - as a method of war.
The UN Security Council has demanded all parties end the indiscriminate use of weapons in populated areas, but civilians continue to die in their thousands. Many have been killed by barrel bombs dropped by government aircraft on gatherings in rebel-held areas - attacks which the UN says may constitute massacres.
4. Chemical weapons
Hundreds of people were killed in August 2013 after rockets filled with the nerve agent sarin were fired at several suburbs of Damascus. Western powers said it could only have been carried out by Syria's government, but the government blamed rebel forces.
Facing the prospect of US military intervention, President Assad agreed to the complete removal and destruction of Syria's chemical weapons arsenal.
The operation was completed the following year, but the Organisation for the Prohibition of Chemical Weapons (OPCW) has continued to document the use of toxic chemicals in the conflict. Investigators found chlorine was used "systematically and repeatedly" in deadly attacks on rebel-held areas between April and July 2014.
5. Humanitarian crisis
More than 4.5 million people have fled Syria since the start of the conflict, most of them women and children. Neighbouring Lebanon, Jordan and Turkey have struggled to cope with one of the largest refugee exoduses in recent history. About 10% of Syrian refugees have sought safety in Europe, sowing political divisions as countries argue over sharing the burden.
A further 6.5 million people are internally displaced inside Syria, 1.2 million were driven from their homes in 2015 alone.