As Syrians vote for president on Tuesday, here's a look at some of the key events in the country since the uprising began:
— March 2011: Protests erupt in the city of Daraa over security forces' detention of a group of boys accused of painting anti-government graffiti on the walls of their school. On March 18, security forces open fire on a protest in this southern city, killing four people in what activists regard as the first deaths of the uprising. Demonstrations spread, as does the crackdown by President Bashar Assad's forces.
— April 2011: Security forces raid a sit-in in Syria's third-largest city, Homs, where thousands of people tried to create the mood of Cairo's Tahrir Square that was the epicenter of protests against Egypt's autocrat Hosni Mubarak.
— June 2011: Police and soldiers in Jisr al-Shughour in northeastern Syria join forces with the protesters they were ordered to shoot, and the uprising claims control of a town for the first time. Elite government troops, tanks and helicopters retake the town within days.
— August 2011: President Barack Obama calls on Assad to resign and orders Syrian government assets frozen.
— July 2012: A bombing at the Syrian national security building in Damascus during a high-level government crisis meeting kills four top officials, including Assad's brother-in-law and the defense minister.
— Summer 2012: Fighting spreads to Aleppo, Syria's largest city and its former commercial capital. Over time, rebels seize control of about half of the city, but the battle there rages to this day, leaving much of Aleppo in ruins.
— August 2012: Kofi Annan quits as U.N.-Arab League envoy after his attempts to broker a cease-fire failed. Obama says the use of chemical weapons in Syria would be a "red line" that would change his thinking about military action.
— November 2012: The Syrian National Coalition is created, bringing together the main opposition factions. The umbrella group is hampered from the outset by crippling infighting and accusations that its members are out-of-touch exiles.
— March 2013: After advancing in the north, rebel forces capture Raqqa, a city of 500,000 people on the Euphrates River and the first major population center controlled by the opposition. That month, the number of U.N.-registered Syrian refugees tops 1 million, half of them children.
— May-June 2013: Regaining ground from rebels with the help of thousands of Lebanese Hezbollah fighters, Assad's forces re-capture the strategic town of Qusair near border with Lebanon.
— June 2013: U.S. officials conclude that Assad's forces had used chemical weapons against the opposition. Obama authorizes direct support for the rebels.
— August-September 2013: A chemical weapons attack in the Damascus suburbs kills hundreds. Obama, blaming Assad's government, says the U.S. has a responsibility to respond and puts it up to a vote in Congress. Russia proposes instead that Syria give up its chemical weapons, averting military strikes.
— September 2013: Eleven rebel groups leave the Syrian National Coalition. Seven of them later form their own alliance, the Islamic Front, intended to eventually create an Islamic state.
— October 2013: Syria destroys its chemical weapons production equipment. The number of Syrian refugees registered with the U.N. tops 2 million.
— January 2014: Infighting among rebels spreads, pitting a variety of Islamic groups and moderate factions against the al-Qaida-breakaway Islamic State of Iraq and the Levant. The first batch of toxic chemicals is shipped out of Syria.
— February: Two rounds of peace talks led by U.N.-Arab League mediator Lakhdar Brahimi in Geneva end without a breakthrough.
— March 21: Syrian rebels launch an offensive in the coastal province of Latakia, capturing the border point with Turkey in the Syrian town of Kassab.
— April 9: Syrian troops backed by Hezbollah fighters capture Rankous, the last major town in the strategic Qalamoun mountain that borders Lebanon.
— April 12: Syrian state media and activists say that the central village of Kfar Zeita was subjected to a poison gas attack that injured scores of people. Both sides blame each other for the attack.
— May 9: Rebels withdraw from the old quarter of the central city of Homs in a significant symbolic victory for the government, putting the area that had been under siege for more than a year firmly in government hands.
— May 13: Brahimi resigns as U.N.-Arab League envoy to Syria, marking a second failure by the United Nations and Arab League to end the country's civil war.
— June. 3: Syrians vote to elect one of three candidates running in the presidential elections, a vote Assad is widely expected to win.