The civil war that has engulfed Syria and brought charges of using chemical weapons on civilians began as a civil protest in the city of Homs. But a tough crackdown by the government of Bashar al-Assad has escalated violently and has drawn in a bewildering array of religious factions, rival Islamic groups and other nations.
Here's a profile of the main players in the Syrian struggle:
On the government side:
Assad regime. It was founded by Hafez al-Assad. He died in 2000 and his son, Bashar al-Assad, has ruled the country since. The family-run government brooks no opposition.
Alawites. The Assad family is a member of the Alawite sect, an offshoot of the Shiite branch of Islam. The Alawites are a minority in Syria, but dominate the government and the military and are fiercely loyal to the Assad family.
Hezbollah. The Shiite group is based in Lebanon and has been armed by Iran and hardened by years of battling Israeli troops. Hezbollah, which depends on the Assad regime and Iran for its weapons, has crossed into Syria and joined the battle against the rebels. The group's added punch has helped Assad's military blunt the rebels' momentum and begin rolling back rebel advances. The U.S. considers Hezbollah to be a terrorist organization.
Iran. The Shiite country has been Assad's closest ally in the civil war, helping to train its troops and sending plane-loads of arms on a regular basis.
On the opposition side:
Free Syrian Army. The moderate force emerged from the street protests and initial Syrian army defections to take on Assad's force, but is badly divided among different factions.
Sunnis. The Sunnis are a majority in Syria, but have long been marginalized by the regime. The ranks of the Free Syrian Army are overwhelmingly Sunni.
Jabhat al Nusra. A radical Islamic force that has pledged allegiance to al Qaeda, has attracted thousands of militant Muslims from around the world, received money and weapons from supporters, and become the rebels' most effective fighting force. It is imposing Sharia law in areas it occupies and has skirmished with the Free Syrian Army, at times.
Gulf States. Saudi Arabia and Qatar, which are largely Sunni monarchies, have been eager to counter the Shiite influence of Iran. They have poured weapons and money to rebel fighters, including militant Islamists over the objections of the U.S.
Turkey and Jordan. Syria's neighbors have become refuges for hundreds of thousands of Syrian refugees and a conduit for arms intended for rebels.
Caught in the middle:
Lebanon. Syria's smaller neighbor has a history of civil war and violent outbursts among its Shiite, Sunni and Christian populations. There have been bombings of Shiite neighborhoods in retaliation for Hezbollah aiding Assad and officials fear the potential of Syria's civil strife spilling into Lebanon.