Ian_W
Banned
I think ISIS' best strategy would be to not make big news or declare any caliphates so the US doesn't get involved and focus on overthrowing Assad, after Syria has completely fallen apart they could easily mop up the disunited rebel groups.
The problem with this strategy is that it doesnt do enough to differentiate ISIS from al Qaeda - remember, ISIS are the old al Qaeda in Iraq, who intervened in Syria against al Qaeda in Syria against the orders of al Qaeda hq in Afghanistan.
Their initial Syrian campaigns, against the generally terribly bad Syrian Army of Assad (*), got them enough loot to leverage into the successful campaign against Mosul.
I dont think that is a viable strategy, as they are competing for the same pool of recruits and money as a number of other Sunni jihadist groups - going for the big brass ring of the Caliphate is the way they differentiate themselves from mainline al Qaeda.
(*) Briefly, Syria is mostly Sunni. Assad is an Alawite. Good Syrian Army units are very good - the Defense of Deir ez-Zour air base is one of the finest deeds of arms I know of, with the airbase being held in face of a IS siege from July 2014 to September 2017. But regular Syrian Army forces are terribly bad, and pro-Assad militias not much better.