Syria's complex civil war, which now involves numerous international actors and terrorist groups, began with pro-democracy protests in March 2011 against the authoritarian rule of President Bashar al-Assad. Since then over 250,000 people have lost their lives and millions of Syrians have been displaced both internally and externally.
The 'red line'
Despite having declared the use of chemical weapons a 'red line', President Barack Obama did not take military action against Syria after the country's government used chemical weapons against its own people in Damascus in August 2013.
Instead, President Assad agreed to dismantle his arsenal of chemical weapons as part of a deal that came about after an apparently unprepared remark by Secretary of State John Kerry in September 2013 that the U.S may not take military action if the weapons were dismantled and destroyed.
Stalemate and a power vacuum
With Syria's opposition forces fractured and the Assad regime having lost significant ground, the terror group ISIS emerged and declared a caliphate in Syria and Iraq in June 2014.
U.S led coalition forces began airstrikes against ISIS targets in September 2014, while Russia began supporting the Assad regime against its opponents through airstrikes in September 2015. The Kremlin announced a pull back in March 2016, but its brief involvement helped the Assad regime regain a foothold in some key areas and consolidate what is left of its power.
Peace talks aimed at finding a political solution to the conflict began in early 2016, while a cessation of hostilities was declared in March.