Syria's conflict enters its eighth year Thursday, with President Bashar Assad's forces fighting to drive rebels from their last bastion near the capital, Damascus, and Turkish forces closing in on the northern Kurdish-held enclave of Afrin.
Assad remains firmly in power seven years after an Arab Spring-inspired uprising that began with peaceful protests but escalated into an armed rebellion following a brutal government crackdown.
Russia and Iran have provided massive aid to Assad's forces, allowing them to advance on a number of fronts in recent years.
The Islamic State group was able to exploit the chaos to seize up to a third of the country at one point, but its self-declared caliphate is now in ruins, with the militants largely confined to a remote area along the Syrian-Iraqi border.
An al-Qaida-linked group dominates the northern Idlib province, while U.S.-backed Kurdish forces hold around a quarter of the country in the northeast.
The fighting in Syria has killed an estimated 400,000 people since 2011 and driven half the population from their homes, with more than 5 million becoming refugees, mainly in neighboring countries. Several rounds of peace talks have done little to stem the bloodshed.
A timeline of key events in the Syria war:
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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 15, a protest is held in Damascus' Old City. On March 18, security forces open fire on a protest in Daraa, killing four people in what activists regard as the first deaths of the uprising. Demonstrations spread, as does the crackdown.
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, the epicenter of protests against Egyptian autocrat Hosni Mubarak.
Aug. 18, 2011: President Barack Obama calls on Assad to resign and orders Syrian government assets frozen.
July 18, 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.
July 2012: Fighting spreads to Aleppo, Syria's largest city and its former commercial capital.
Aug. 20, 2012: Obama says the use of chemical weapons would be a "red line" that would change his calculus on intervening in the civil war.
March 19, 2013: The Syrian government and opposition trade accusations over a gas attack that killed some 26 people, including more than a dozen government soldiers, in the town of Khan al-Assal in northern Syria. A U.N. investigation later finds that sarin nerve gas was used, but does not identify a culprit.
May 2013: Lebanon's Hezbollah group officially joins the Syrian conflict with government forces by attacking and later capturing the border town of Qusair.
Aug. 21, 2013: A chemical attack in the eastern Ghouta suburbs of Damascus kills hundreds of people. The U.S. and others blame the attack on Syrian government forces. Obama threatens punitive strikes but later backs down.
Sept. 27, 2013: The U.N. Security Council orders Syria to account for and destroy its chemical weapons stockpile, following a surprise agreement between Washington and Moscow, averting U.S. strikes.
Oct. 14, 2013: Syria becomes a signatory to the Chemical Weapons Convention, prohibiting it from producing, stockpiling or using chemical weapons.
June 23, 2014: The Organization for the Prohibition of Chemical Weapons says it has removed the last of the Syrian government's chemical weapons. Syrian opposition officials maintain that the government's stocks were not fully accounted for, and that it retained supplies.
June 30, 2014: Islamic State group declares caliphate in areas it controls in Iraq and Syria.
Sept. 23, 2014: The U.S. launches airstrikes on Islamic State targets in Syria.
March 28, 2015: The northwestern city of Idlib falls to Islamist groups led by al-Qaida's affiliate, known as the Nusra Front.
May 6, 2015: Assad acknowledges serious setbacks for his military.
Sept. 30, 2015: Russia begins launching airstrikes in Syria in support of Assad's forces.
August 2016: Turkish forces cross into northern Syria, capturing areas along the border from the Islamic State group.
December 2016: Syrian insurgents evacuate rebel-held eastern neighborhoods of the northern city of Aleppo after a Russia-backed government offensive.
April 4, 2017: At least 58 people are killed in what doctors say could be a nerve gas attack on the town of Khan Sheikhoun in the rebel-held Idlib province. Witnesses say the attack was carried out by either Russian or Syrian Sukhoi jets. Moscow and Damascus deny responsibility.
April 6, 2017: The U.S. fires a barrage of cruise missiles into Syria in retaliation for the Khan Sheikhoun attack, in the first direct American assault on the Syrian government.
May 2017: Rebels withdraw from the last neighborhood they controlled in the city of Homs, once dubbed the capital of the revolution.
Jan 20, 2018: Turkey begins a major military operation against Kurdish fighters in Syria's northern enclave of Afrin.
February 2018: Syrian government forces launch a massive operation to drive rebels from eastern Ghouta.
AP
