If you look the time lapse map of syria. ISiS and Al nusera/AQ, HTQ etc where not present in Assad govenment controlled territory. But the US backed SDF (FSA,AQ, ISIS they change their insignia based on the wind direction and pay) and Turkey backed terrorists areas near Turkey border. Its from those non-Assad controlled territories that made a charge towards allepo and Damascus. We where told from media that these are good rebels, just like the mujahdeen in Afghanistan.
So the US knew who exactly they are dealing with and they used them to get regime change objective. The monster that CIA created was let loose and that monster couldn't have a safe zone in Assad controlled territory. So they where there in the US controlled territory. Those factions that cannot be controlled where killed but was kept trained and paid for years to topple Assad.
Only the Kurds where good but will be slaughtered by Turkey backed terrorists. Just before the Russia ukraine war. Turkey invaded Syria and where bombing the kurds. The US forces did not protect them. The kurds appealed to Russia and Russia then negotiated a peace agreement with turkey, with russian forces patrolling the areas bordering the kurds controlled territory and Turkey new controlled territory.
But Erdogan because he controls the Bosphorus Strait has huge leverage against Nato and Russia. Shortly after Russia was occupied with Ukraine war. Turkey launched air strikes and ceased more territory. While the US just let it happen and continue to do nothing as Turkey continues to bomb them as we speak. So the Kurds and Syrian Christians are going to be slaughtered.
Rebels supported by Turkish air power fired on a Kurdish-controlled city in northern Syria, pitting proxies of the U.S. and Turkey — NATO allies — against each other.
www.nytimes.com