When fighting on multiple fronts, it helps to have a single objective that benefits but contrasts with the purpose of other groups. This, in large part, is the ISIL advantage. Its goals, unmatched by other groups, entangle historic conflicts, civil conflicts, and regional struggles for hegemony.
Unlike other Syrian opposition forces, ISIL went after resource rich areas that enabled it to pay its own way. It controls these areas through force and cooperation. It built an oil smuggling network using Turkey’s southeastern border with Syria and Iran to access a black market returning $1-2 millions a day! It taxes population centers in which it allows businesses to operate.
It conceals its fighters and operations by embedding with the Syria/Iraq Sunni population, the traditional enemies of the region’s Shia governments. It controls Syrian territory al-Assad is unable to defend and Iranian territory Maliki ignored.
It’s psychological appeal reinforces its power: imagine 30,000 young men, armed and untouchable, paid regularly, possessing absolute power shared only with each other; the power trip, reinforced by killing, breaks down ethics. The power to kill is king! (It resonates: see al-Assad’s 190,000 civilian dead; ISIL’s massacre of 1700 Iran regulars, the vicious taunt of the beheadings. )
Western journalists ask old questions of strategy; this is a new phenomena. Facts and context are better for its understanding than reports of speculation and political calculation.