A severely hobbled Hezbollah was in no position to help defend former Syrian President Bashar Assad, a longtime ally, from the lightning-fast insurgency that toppled him. With Assad gone, the militant group based in Lebanon is even weaker.

The ascendance of Sunni Islamist rebels in Syria should be viewed with great caution by Western powers, but the Assad regime’s collapse disables a critical node in Iran’s regional proxy network, a counterterrorism expert explains.

The Syrian regime’s collapse came more quickly than the rebels had dreamed — the circumstances were both serendipitous and part of a larger global realignment.