The Campaign by Syrian Rebels to Topple al-Assad Was Swift

The government of President Bashar al-Assad of Syria, which had kept rebel forces at bay for more than a decade with Iranian and Russian military support, collapsed with astonishing speed on Sunday morning after an advance by opposition forces on the capital, Damascus.

Mr. al-Assad fled the country as rebel forces closed in on Damascus, according to the Russian government, one of his main allies. The whereabouts of Mr. al-Assad, an authoritarian leader who had gassed his own people during a 13-year civil war, were unclear early on Sunday.

The rebel offensive had lasted less than two weeks.

The Russian foreign ministry said Mr. al-Assad had “decided to leave the presidential post and depart the country” after talks with other “parties to the conflict.” He had given instructions to transfer power peacefully, the ministry said.

There was no comment from Mr. al-Assad. His former prime minister, Mohammad Ghazi al-Jalali, stayed behind and said he was ready to cooperate with the rebels. The opposition forces swept into Damascus with little apparent resistance from the Syrian military, seizing control of government buildings and the state broadcaster.

For years, the Syrian civil war — which had erupted in tandem with the anti-government Arab Spring uprisings in 2011 and continued with horrific violence until 2017 — remained unresolved, but relatively stagnant.

Then, in October 2023, Hamas attacked Israel, and the subsequent war upended the regional chess board of the Middle East. The Syrian rebels struck at a moment of weakness for Mr. al-Assad’s main allies: Iran, Russia and Hezbollah, the militant group based in Lebanon and backed by Iran.