The numbers behind Syria's civil war are staggering: Well over 100,000 people have died, according to the United Nations. More than 6 million, nearly a third of Syria's population, have been forced from their homes. Two million, half of them children, have fled Syria entirely.
The war's human toll is still rising as the war drags on, two and a half years after it began, and the world's allegiances have been divvied up between the hodgepodge of rebel groups and Syrian President Bashar al-Assad's regime. The U.S., United Kingdom, France, Turkey and the Arab Gulf states have sided with the rebels, while Russia, Iran and Hezbollah support Assad's regime.
Now, that regime stands accused by the West of unleashing chemical weapons to kill its own people — but the West is split on whether to intervene.
President Barack Obama, who last year called the use of chemical weapons a "red line," wants Congress to authorize a military strike on Syria. But the memory of the U.S. invasion of Iraq a decade ago, based on faulty intelligence of phantom weapons of mass destruction, looms large.
But who is Assad, whom U.S. Secretary of State John Kerry has put in a league with Adolf Hitler, and who are the rebels fighting him? What began this war, and why is it still raging? Why are we talking about chemical weapons, and why might we intervene?
And how, exactly, did we get to this point?
Behind the Assad Dynasty
Bashar al-Assad came to power in 2000 after the death of his father, Hafez al-Assad. Hafez had himself come to lead Syria with a 1970 coup, installing a regime during which he would systematically shore up his own power. But while Bashar is the scion of an autocrat who brutally ruled for three decades, he became the heir apparent only by accident.
Hafez modernized Syria in some respects, and his relentless secularism was popular with religious minorities. But he also ruled with an iron fist, crushing dissent, notably after the Muslim Brotherhood rose to prominence in 1979. (His 1982 siege in the restive city of Hama killed thousands.) Hafez had groomed his charismatic son Basil to succeed him, but his plans were dashed when Basil died in a car crash in 1994.
Bashar, then a fledgling eye doctor living in London, was their father's Plan B.
After he took power on his father's death in 2000, he assumed a position atop a power structure his late father had carefully orchestrated, while his more hardline brother Maher took a post heading two elite military regiments. Bashar, along with his wife Asma, a London-raised and Vogue-profiled former JPMorgan stockbroker, appeared set to herald in a new era of a more modern, less repressive Syria.
That all changed when the nascent Arab Spring arrived in Syria in early 2011.
Arab Spring and Beyond: Syria's Civil War
When Arab Spring protests began to ripple across the region early in 2011, Syria was a relative latecomer — in large part due to its strict security measures. The country had been under emergency law for decades, the entire duration of both Assads' regimes.
But under the surface, there was certainly discontent: Economic woes and unemployment plagued the country, exacerbated by a drought that had sent out-of-work farmers into already-struggling cities, and in the capital Damascus, even the relatively well-off Syrians resented the regime's political repression.
Small-scale protests broke out in Syria in early 2011, soon after unrest began roiling its neighbors, but it was the violent crackdown that March in the city of Daraa that began to trigger broader unrest. Demonstrators called for reforms — and Assad promised some, recognizing the need for conciliatory gestures. (Arab Spring protests had just forced Egypt's long-ensconced Hosni Mubarak from power.) He lifted the emergency law, fulfilling one of the protesters' key demands, but his harsh crackdowns continued. So did the unrest.
Days later, after deadly clashes, army tanks rolled into Daraa. Amid the siege, some troops defected, refusing to fire on civilians. Unrest spread, and as it did, the crackdowns grew harsher, defections more widespread.
What started as popular Arab Spring discontent by protesters calling for reforms gradually became a full-fledged civil war. By fall of 2012, the fighting had spread to Aleppo, Syria's largest city, and to Damascus, the seat of Assad's power. The country was being carved up into a patchwork of swaths controlled variously by regime forces or rebel fighters.
Soon, Assad's regime and rebels began to accuse one another of having used chemical weapons.
The Rebels: Who They Are
Syria's rebel fighters are hardly a unified front. Rather, they are a myriad collection of disparate groups, many of them at odds with each other, who happen to be fighting a common enemy: Assad.
The U.S. has resisted arming the rebels, for fear weapons could fall into terrorists' hands or otherwise empower the forces' more brutal elements. Many onlookers, including Kerry, fear that scenario could become more likely as foreign terrorists head to Syria, hoping to exploit its ongoing crisis.
Of the scores of rebel factions, here are some of the major players:
Still other rebel fighters have separate aims of their own — the ethnic Kurdish militias, for instance, seeking to protect Kurdish identity and independence — while plenty of others are fighting the Assad regime while unaligned with one of the more formal rebel groups. (A helpful breakdown is here.)
What We Know About Chemical Weapons...
Accusations by both the Syrian rebels and the Assad regime of chemical weapons use ramped up in March, but it wasn't until June that the U.S. said it had confirmed that the Assad regime had used chemical weapons. Meanwhile the West pressed Assad to let in U.N. weapons inspectors, and eventually he did, for a very limited inspection.
On August 21, while the U.N. team was in Syria, an apparent gas attack outside Damascus left an estimated hundreds of civilians dead. The Assad regime agreed four days later to grant the U.N. team access to that site. The team, now out of Syria, is still wrapping up its probe.
The U.S. said it knows beyond a reasonable doubt that Assad ordered an August 21 chemical weapons attack that it said killed 1,429 civilians. An unclassified intelligence report elaborated on that claim, but the U.S. has released no hard evidence to corroborate it.
French intelligence also indicated an attack by Assad, but its findings differed and put the death toll lower. Like U.S. intel, the French report was accompanied by little concrete evidence. A leading Syrian opposition group also estimated the death toll much lower, at just over 500 dead.
Assad dismissed all such accusations in an interview with French newspaper Le Figaro, challenging the U.S. and France to provide proof he launched a chemical weapons attack.
...And What We Don't Know
For now, the circumstances and death toll of the apparent attack remain unclear. The intelligence disparities, as well as the lack of unclassified substantiating evidence, have evoked still-fresh memories of the run-up to the U.S. invasion of Iraq in 2003 and all the purportedly "slam-dunk" intelligence indicating Saddam Hussein's regime there had weapons of mass destruction.
In Syria, the U.S. and its allies generally agree that only Assad would have been capable of launching the August 21 attack; only Russia has blamed the rebels. But the U.S. and its allies can't agree on a motive for why Assad might have done it.
Intelligence officials told the Associated Press that the intelligence linking the Assad regime to the attack was "no slam-dunk," and the specificity of the U.S. report's claims, particularly its death toll estimate of 1,429, are being eyed skeptically. "Put simply, there is no way in hell the U.S. intelligence community could credibly have made an estimate this exact," former senior defense official Anthony Cordesman wrote of that number.
But as the world awaits the results of the U.N. investigation, there is frustratingly little information from Syria about the apparent attack, largely because of how dangerous Syria is for journalists and how off-limits it is to foreign ones.
For now, there is little for the U.S. and Syrians to do but wait — for Obama to wrangle Congress into voting for a military strike, for other Western allies to support it, for the U.N. team of chemical weapons investigators to finish its probe and for something, anything, to break the stalemate into which Syria's civil war has fallen.