All of those people didn't co-exist in fact were belligerents in the civil war that erupted.
There wasn't a US coalition until we and that coalition finally coordinated to get overtly involved on the ground in Iraq and Syria against the Islamic State...and that didn't occur until November of 2015.If the US coalition were serious about defeating ISIS , they would have done it quickly .
No, Russia had been moving into Syria for some time. They had secured oil exploration deals in the Med off the Syrian cost and have been protecting those assets with permanent military bases….an air base in Hmeimim and a naval base in Tartous.Russia took a few weeks to turn the whole war around in favor of Assad.