Bob
If it's coming to naught it's not just because of the IS scourge, it's mainly because the various tribes of the region and the two factions of the religion of peace appear to have inordinate difficulty in finding reasons not to slaughter each other. The fact that the Shi-ite side appears to be perfectly happy to lob unaimed barrel bombs indiscriminately into Sunni areas is a bit of a giveaway.
They're not helped by one side being funded by those nice people in Iran (and what's left of Syria) and the other by those nicely balanced folk in Saudi and Qatar.
At this point, it ain't the fault of "the West". People can burble on about Sykes-Picot and Bliar and breaking it and owning it all they want, but that's just an am-dram version of "something must be done". The fundamental bottom line is that a sizeable fraction of these folk can't actually get over their local hatreds to get on with the enjoyable business of living. Instead they'd rather compete in a "Who owns the fewest heads?" competition, funded and encouraged by their rather paranoid neighbours.
Regrettably, no outside force is going to solve this one and certainly not one based on "western" boots on the ground.