"That speech had a catastrophic impact," the International Crisis Group's Peter Harling told CNN last year. "People who wanted to support the regime at the time were shocked."
Two days later, weekly anti-government protests began across Syria. Calls for reforms soon escalated into calls for the removal of the entire al-Assad regime.
Now, armed rebels have vowed to accept nothing less than al-Assad's ouster, while the Syrian government has labeled them terrorists and vowed not to back down.
The United Nations estimates that the fighting has claimed more than 100,000 lives.
4. OK, but that all started more than two years ago. Why do some people think the United States needs to take action now?
Talking about Syria last year, President Barack Obama said "a red line for us is we start seeing a whole bunch of chemical weapons moving around or being utilized."
The implication was clear. If Syria uses chemical weapons in the civil war, the United States will have to do something.
Now, the White House says it looks like Syria has used chemical weapons against its own people. So here we are.
What will Obama do in response? Whatever it is, it's time to sit up and take notice, because this news story is moving to another level.
5. What makes chemical weapons a game changer?
Some argue that conventional weapons like guns or bombs also have a massive human toll. They say chemical weapons shouldn't be a turning point for the world to act.
But the White House maintains that they're a game changer.
"The use of chemical weapons is contrary to the standards adopted by the vast majority of nations and international efforts since World War I to eliminate the use of such weapons ... The use of these weapons on a mass scale and a threat of proliferation is a threat to our national interests and a concern to the entire world," White House spokesman Jay Carney said this week.
6. Why didn't the United States just send a bunch of weapons to the opposition when it had the chance?
In June, the United States said it would send the rebels small arms, ammunition and potentially anti-tank weapons. But that was long after the unrest started. Why the delay?
Well, some argue that sending weapons to a region of the world that also contains Islamic extremists is risky business.
Many of the rebel fighters are militants with pro-al-Qaida sympathies, the same stripe of militants America has battled in Iraq and Afghanistan.
The Syria rebels have promised U.S. and European officials that any military weaponry they get won't end up in extremists' hands. But that hasn't quelled criticism from some quarters that arming the rebels is a dangerous risk.
Russian President Vladimir Putin has slammed the decision to arm the opposition. At an economic forum in June, he cautioned -- "Where will those weapons end up?"
7. What's the deal with Russia? Why are they criticizing the U.S.?