March 2011 -- The first major protests in Syria begin with a "Day of Dignity" in Damascus, demanding the release of political prisoners. A number of people are shot dead by security forces at a similar protest in Daraa, leading to clashes and unrest.
May 2011 -- Government tanks roll into Homs, Daraa and areas of Damascus in a bid to quash anti-regime protests, resulting in tighter sanctions by the United States.
July 2011 -- Syrian President Bashar al-Assad fires the governor of Hama following a mass demonstration there. The government sends in troops, and hundreds are reported killed.
August 2011 -- President Barack Obama calls on al-Assad to step down for the first time, also issuing an executive order immediately freezing all assets of the Syrian government subject to U.S. jurisdiction.
November 2011 -- The Arab League suspends Syria's membership, effective Nov. 16, 2011.
February 2012 -- The U.S. closes its embassy in Damascus, citing security concerns, as Russia and China again block a U.N. draft resolution condemning Syria's actions.
March 2012 -- Government troops push into Homs. After a year of fighting, the U.N. believes more than 8,000 people have died, although activists put the number closer to 10,000.
June 2012 -- The United Nations suspends its mission in Syria, citing security concerns. On June 21, Syrian government forces shoot down a Turkish jet near its border, prompting an emergency NATO meeting.
July 2012 -- Top Assad aides are killed in the bombing of the National Security building in Damacus by rebel forces. Rebels says it's retribution for the massacre of roughly 200 people in Tresmeh, a small Syrian farming village, five days earlier.
August 2012 -- The United Nations accuses Syria of war crimes in the massacre of more than 100 civilians, half of them children, in the village of Houla in May 2012.
December 2012 -- Rebels make gains in Syria's capital, taking over military bases in Damascus against weakened government forces.
January 2013 -- Assad announces he will not step down and that his vision of Syria's future includes a new constitution and an end to support for the opposition, which he calls terrorists. The opposition refuses to work with Assad's government.
February 2013 -- The U.N. Security Council estimates that the number of civilians killed in Syria's two-year civil war is approaching 70,000.
March 2013 -- The rebel coalition elects an interim leader, Ghassan Hitto, who spent much of his life in the United States, and holds dual U.S. and Syrian citizenship. Following the seize of the northern city of Raqqa, Syrian planes bomb Raqqa.
April 2013 -- Britain and France inform the United Nations that there is credible evidence that Syria has used chemical weapons against rebel forces. Defense Secretary Chuck Hagel says the U.S. has evidence of sarin gas being used on a small scale.
May 19, 2013 -- Hezbollah, a long-standing ally of Syria, sends thousands of men to support Assad forces and fight against the rebels in parts of the strategic border town of Qusair.
May 27, 2013 -- The European Union decides to lift the arms embargo on the Syrian opposition while maintaining all other sanctions against Assad's regime.
June 5, 2013 -- After months of heavy fighting, Hezbollah fighters help Syrian forces capture the city of Qusair.
June 13, 2013 -- The continuing violence in Syria has killed nearly 93,000 people, according to new estimates by the United Nations.
June 13, 2013 -- The United States concludes the Syrian government has used chemical weapons in its fight against opposition forces, and President Obama authorizes direct U.S. military support to the rebels.
July 2013 -- Ahmad al-Jarba, a little-known tribal leader, is elected to head the Syrian Opposition Coalition.
August 2013: More than 100,000 Syrians have been killed in the ongoing civil war, according to updated figures from the United Nations.
Aug. 21, 2013 -- Government forces are accused of a nerve gas attack in a Damascus suburb that killed large numbers of civilians as they slept and packed makeshift hospitals with hundreds of victims convulsing and gasping for breath. Assad denies any involvement.
Aug. 26, 2013 -- U.N. inspectors are shot at as they attempt to investigate the site of the alleged nerve gas attack one day after the Syrian government finally relented and allowed full access inside.
Aug. 30, 2013: Secretary of State John Kerry says that U.S. intelligence information found that 1,429 people were killed in the Aug. 21, 2013, chemical weapons attack in Syria, including at least 426 children. A preliminary U.S. government assessment asserted "with high confidence that the Syrian government carried out the chemical weapons attack against opposition elements in the Damascus suburbs," he says.
Aug. 30, 2013: The White House releases a map of the U.S. government's assessment of the Syrian government's use of chemical weapons on Aug. 21, 2013.
Aug. 31, 2013: President Barack Obama says that the United States "should take military action against Syrian targets" in a Rose Garden address. However, he says he will seek Congressional approval when Congress returns from recess.
Sept. 1, 2013: Secretary of State John Kerry says blood and hair samples collected from Damascus by first responders and tested by the U.S. have tested positive for sarin. Kerry argued the evidence strengthens President Barack Obama's call for military strikes on Syria.
June 2014 -- ISIS (Islamic State of Iraq and Syria) militants declare they have established a "caliphate" in the territory they control, stretching from Aleppo in northwestern Syria to the eastern Iraqi province of Diyala. They later rename their group Islamic State.
August 2014 -- The United Nations says Islamic State militants have committed "mass atrocities" in Syria. Tabqa airbase, near the northern city of Raqqa, falls to the extremist group.
Sept. 22, 2014 -- The United States and several Arab nations begin airstrikes against Islamic State targets in Syria. The number of casualties was not immediately clear. But U.S. Central Command said the strikes damaged or destroyed Islamic State fighters, training compounds, command-and-control facilities, a finance center and supply trucks.