Syria’s freedom protesters had asked for a better future for everyone, including for him, but received only bullets in reply. He conceded to me that the crackdown had been wrong and had forced Syrians to take up arms, and he told me that Assad had tried to stop the attacks, only to be overruled by his intelligence services. But when I asked about the use of sarin gas against civilians in August 2013, I clearly crossed a line. His demeanor changed, and a menacing smile crept onto his face. “We both know the who and why,” he snapped. “Don’t ask questions you know the answer to!”
Assad has deliberately nurtured ISIS, or at least tacitly allowed its rise, as a means of marginalizing more moderate rebels whom outside powers like the US might have supported against him. The Syrian dictator and ISIS seem to have made an implicit deal: ISIS temporarily gets a relatively free ride in some chunks of Syria, while Assad gets to weaken his other opponents. This allows Assad to divide the rebels, and to force the world to choose between him and ISIS.
"When Islamic radicals took over Raqqa, the first province to fall under rebels' control in its entirety, it was remarkable that the regime did not follow the same policy it had consistently employed elsewhere," Syrian journalist Hassan Hassan writes, "which is to shower liberated territories with bombs, day and night." Assad left ISIS alone because its very existence made an international intervention to stop his mass murder of Syrians less likely.
If Assad had assaulted ISIS-held territory with the same fervor he brought to the fight against other Syrian rebels, the group almost certainly wouldn't be as strong as it is today.
"ISIS has been a Saudi project," the Atlantic's Steve Clemons quotes a senior Qatari official as saying. The Qataris only (only!) admit to funding Jabhat al-Nusra, which is al-Qaeda's branch in Syria.
The Iraqi and Syrian governments played a major role, but so did the United States, Iran, and Gulf monarchies like Saudi Arabia.
The predominant causes of ISIS's rise in the two countries — internal Iraqi politics and the Syrian civil war itself.