God what a mess..
Tyrant Assad attacked by Free Syrian Army and other groups after a popular uprising. NATO Turkey supports FSA, providing safe haven etc, as does Israel, providing medical assistance as well. Russia, Iran and our friends Iraq support Assad, as does Hezbolah. The UN accuses the FSA of War Crimes. IS wade in from the East like the Mongol hordes and fight FSA and Government forces alike. The US and her friendly Arab allies bomb IS in Syria, collaborating with the FSA along the way, but potentially supporting Assad as well. The tough little Kurds hold out in 'their' territory and fight off everyone who wants some.
The world has gone mad. I actually think we are probably better off waiting for IS to finish their Syrian press and then try and take on Turkey or Israel. The 'Coaltition' can play a secondary role (if the US is capable) while some real regional grunt takes the gloves off, suiting everyone.
IS have numbers, and weapons, and no doubt capable leadership and motivation. But they have been lucky as well, both the Iraqis and Syrian government forces are a shadow of their former selves. Up against very pissed off Turks or Israelis (or both) with US (possibly dont want the UN in on this one..) support, and they'll get smoked.