There were indications that Bashar Assad’s regime could struggle to maintain its grip on power in Syria — but the military assault that ended his family’s more than 50-year reign happened much faster than some experts expected.

Assad relied on allies to maintain power during the civil war that commenced more than a decade ago, but when his forces were faced with a new threat starting in late November, they were on their own. Iran, Hezbollah, and Russia did not come to his aid, though Moscow did purportedly allow him to seek refuge there.