Backgrounder: Course of events in Syria's five-year civil war

Tuesday marks the fifth anniversary of the start of the Syria civil war. The following are the major events that unfolded during the course of the war.

-- In March 2011, protests launch in Daraa in southern Syria and later spread to Damascus and other Syrian cities, prompting the government to crackdown on opposition activists, which gradually developed into armed rebellions against the government.

The first rebel group was formed in the same year under the name of the Free Syrian Army, which was said to have been formed of military defectors. Also in 2011, the United States and European Union imposed sanctions on the Syrian government.

-- In July 2012: Fighting spreads to Aleppo, Syria's largest city and its former commercial capital.

-- In August 2012: Kofi Annan quits as UN-Arab League envoy after his attempts to broker a cease-fire failed.

-- In August, 2013, several opposition-controlled areas in the suburbs around Damascus are struck by rockets containing the chemical agent sarin, killing as many as 1,400 people. Both the opposition and the government trade accusations.

-- In October 2013, officials with the Organization for the Prohibition of Chemical Weapons arrive in Syria to monitor the dismantlement of the Syrian chemical weapons arsenal, after Damascus officially joined the Prohibition of Chemical Weapons Convention.

-- In June 2014, Syria's incumbent President Bashar al-Assad wins a third seven-year term in office in presidential elections, which were dismissed by the opposition and their western backers as a "farce."

-- In September 2014, the United States and a number of Arab countries launch joint airstrikes against Syria as part of the U.S.-led anti-terror coalition.

The airstrikes were largely focused on Islamic State-controlled areas in northern Syria. Such strikes were also crucial for the Kurds, who made gains against IS backed by the U.S. air cover.

-- The year 2015 witnessed a surge in the number of refugees fleeing their homes, causing what is now known as the refugee crisis in Europe.

-- On Sept. 30, 2015, Russia raised its involvement in the Syria crisis and began to bomb both IS targets and rebels forces.

-- On Feb. 27, 2016, a cease-fire begins after a cessation of hostilities plan backed by Russia and the United States goes into effect.

-- On March 9: UN Special Envoy for Syria Staffan de Mistura says indirect peace talks will resume in Geneva on March 14. Endi