What began as a peaceful uprising against Syria's President Bashar al-Assad five years ago became a full-scale civil war that has left more than 250,000 people dead, devastated the country and drawn in global powers.
Why is there a war in Syria?
Long before the conflict began, most Syrians complained about high unemployment, widespread corruption, a lack of political freedom, and state repression under President Bashar al-Assad, who succeeded his father, Hafez, in 2000.
Protests in the southern city of Deraa in March 2011 were suppressed by security forces
In March 2011, pro-democracy demonstrations inspired by the Arab Spring erupted in the southern city of Deraa. The government's use of deadly force to crush the dissent soon triggered nationwide protests demanding the president's resignation.
As the unrest spread, the crackdown intensified. Opposition supporters began to take up arms, first to defend themselves and later to expel security forces from their local areas. Mr Assad vowed to crush "foreign-backed terrorism" and restore state control.
The city of Homs, dubbed "the capital of the revolution" suffered widespread destruction
The violence rapidly escalated and the country descended into civil war as hundreds of rebel brigades were formed to battle government forces for control of the country.
Why has the war lasted so long?
Government forces have lost control of large swathes of the country to various armed groups
France and the UK have called on the UN to begin air drops of humanitarian aid to besieged areas in Syria. Last month, the International Syria Support Group (ISSG) set a deadline of 1 June for the distribution of urgent humanitarian supplies. But only a small amount of aid was delivered on Wednesday and a convoy to the town of Darayya near Damascus did not even carry food. The UN Security Council will meet on Friday to discuss the air drops.
What's being done to end the fighting?