The timing was probably not a coincidence, falling as it did on two anniversaries. August 18, 2011, was when President Obama first demanded Syrian president Bashar al-Assad step aside, and August 20 last year was when Obama warned that the use of chemical weapons would “change my calculus.” It was a year to the day after Obama’s warning that Assad launched what is to date the regime’s largest chemical weapons attack. At least a thousand people are dead, likely more, in several Damascus suburbs and outlying towns. The video reports from Syria are chilling—children foaming at the mouth, their unblinking eyes full of terror, their contorted limbs frozen like broken dolls.

Yes, yes, it’s terrible, say many, but why would Assad be so foolish as to use his unconventional arsenal when a U.N. investigating team is already in the country collecting evidence on past use of chemical weapons? Well, Assad is not a fool: The purpose of waging an attack under the watchful eyes of the U.N. is to show his adversaries that the international community, the Europeans, and even the Americans are not going to help them, no matter what. Assad’s message to the rebels is: In spite of their moral posturing, their stern admonitions, even their revulsion and horror at watching children paralyzed by nerve agents, your Western friends won’t help you. Indeed, they are so craven, so eager for a reason to do nothing, they will suggest that the chemical attack was perhaps a ploy—that to get them to enter the war on your side, you killed your own children.

There’s also a military logic at work in Assad’s chemical attack last week. For months, the regime has been shelling these neighborhoods northeast of Damascus, explains Tony Badran, research fellow at the Foundation for Defense of Democracies. “But every time the regime tries to enter—armored units or infantry—they’re repelled by rebel fighters. Last week’s attacks, and these areas were [also] subjected to chemical weapons attacks in the spring, are intended to disrupt rebel defenses.”

There’s a strategic purpose, too. “These neighborhoods are not far from Mt. Qassioun,” says Badran, “which is the military’s center of gravity. It’s not just a military base, but also high ground from which the regime can easily fire on the rebels.” Moreover, Badran explains, “the neighborhoods attacked last week overlook the Damascus-Homs highway, which is one of the regime’s main communications lines. A little further northeast is an airport in Dumayr where the regime is supplied by direct flights from Iran. Therefore, it’s essential Assad establish control over this strategic territory.”

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