Alright /k/, there is something I don't understand. Wikipedia

>>34759839

US and arab money + training, intel, constant influx of new members through Turkey

During the golden days of isis the saa was in a chaotic state. They were throwing all their recources at the battles for the mayor cities in the west of the country (damascus, aleppo, hama, homs, daraa, ..) leaving the eastern parts of the country easy prey for isis. Same for the kurds who back then were basically just tribes all fighting for their own village. Only when they were driven into a corner the kurds figured out they stood a much better chance when teaming up. So they regrouped, held the line and eventually started pushing back isis (alot faster once the us started supporting them). Same for the saa, it took russian airsupport and iranian manpower to stabilise the battle in the west. Only then could the saa regroup and start resisting further advances from isis

Also low morale combined with the terror isis spread (mass executions, torturing, ..) meant most of the time soldiers and tribal warriors would either retreat, surrender or even pledge alliance to isis rather than put up a fight

>>34759839
Truth be told ISIS was never a real threat to Assad. In Syria ISIS focused on fighting the rebels taking land and converting menpower from them. Much of what became ISIS in Syria was rebels defecting.
Assad knew this and so avoided engaging ISIS. More often ISIS was used by the SAA as the anvil to their hammer and vice versa.
That is not to say they collaborated, just that their interests aligned.
Only time ISIS posed a srategical threat to Assad was after they took Palmyra and kept pushing westword from there.

ISIS in it's prime had alot more fighters than it has now. Plus a lot more of their elite war seasoned fighters and leaders were alive.
Quality many times trumps quality.