Syria’s Rebels Struck When Assad’s Allies Were Weakened and Distracted

For years, President Bashar al-Assad of Syria was able to beat back opposition fighters with the help of Russia, Iran and Hezbollah. Now, with those allies weakened or distracted by their own conflicts, rebels have seized the opportunity to shift the balance of power.

The rebel fighters spent months training and preparing for a surprise offensive, but even they may not have predicted how quickly they would advance. On Saturday, the rebels said they had captured almost all of Aleppo, one of Syria’s biggest cities, and they now control a broad stretch of land in the west and northwest of the country, according to the rebels and the Syrian Observatory for Human Rights, a British-based war monitor.

The timing of the assault and its success, analysts say, reveal the vulnerabilities of Mr. al-Assad’s once formidable coalition.

The Syrian civil war started 13 years ago when peaceful anti-government protests were met with brutal crackdowns, escalating into a conflict between forces loyal to Mr. al-Assad and rebels. Over time, the combatants drew support and foreign fighters from regional and international powers.

Iran, Hezbollah and Russia all sent help to the Syrian military. Hezbollah and Iranian-backed fighters battled alongside Syrian forces, Russia and Iran sent military advisers, and Russia carried out intense airstrikes on rebel-held territory.

But today, Iran has been weakened by Israeli airstrikes, battlefield losses by its proxy forces — the so-called axis of resistance — and an economic crisis at home. Hezbollah, one of those proxy forces, has been battered and diminished after 13 months of war with Israel and the killing of its leader, Hassan Nasrallah. And Russia is now nearing the end of its third year of a war of attrition with Ukraine.