How stable is the caliphate of the Islamic State?

In 2013 the Al Qaeda brigades in Syria succeeded in making extensive territorial gains and attained the preeminent position among the rebel groups. The moderate Free Syrian Army fell apart. This provided the opportunity for Al Qaeda to found an Islamic state. As early as the early summer of 2013 the Free Syrian Army was already reporting that Al Qaeda was seeking to found a state of its own in the north of Syria which would also control the border crossing points to Turkey