Assad and the myth of the lesser evil
Bente Scheller'In Raqqa, the only provincial Syrian capital in which ISIS is the sole power, the army didn't hit ISIS' easily identifiable headquarters. This location was formerly the seat of government in Raqqa, so the army should have been more than familiar with its coordinates. Instead, the strikes occurred nearby.
Assad's choice to give up Syria's northern border, in particular, was what made it possible for large numbers of foreign fighters to flood into the country. In establishing his own militias, he forfeited the state's monopoly on the use of force. The West's reluctance to put its weight behind the political opposition and bolster the Free Syrian Army at the right time opened up the field for extremist forces and their supporters.
ISIS can pay salaries, distribute food and, in Raqqa, buy acceptance by providing electricity and taking on all the other usual functions of a state.
A patchwork in northern Syria
By contrast, that was never possible for either the Free Syrian Army or for the Syrian National Coalition in Istanbul, because both oppositional groups lacked the funds that would have enabled them to take a similar course - not to mention the fact that the regime continued to make air strikes even in regions it had long since lost to the rebels. The sole purpose of this was to prevent state-like structures from forming there. That has turned northern Syria into a patchwork in which various local authorities have small areas of control.
Assad has never given any reason to doubt that he's not concerned about Syria, only about himself. Right at the start of the revolution, in the first few months, his troops would spray graffiti in the places targeted by their wrath that read: "Assad or we'll burn the country to the ground." This is indeed the approach he has consistently implemented ever since.'