Syria, Northern Iraq, Yemen and Somalia?

These are all either failed states or on the way to becoming failed states the way things are presently going.

What can stop this?

I'm not sure at this point that anything can stop these nations from unraveling. It's possible if Turkey wanted to invade Northern Syria and Iran wanted to invade Northern Iraq that ISIL(ISIS) could be mostly eliminated. However, I don't think that is going to happen do you?

So, this means that Northern Iraq, Northern Syria and possibly Yemen are going to stay a mess unless one of the bigger nations gets upset enough to change this situation or incorporate those former parts of other nations into themselves.

Otherwise, things will tend to just get worse and worse over there for the average person that doesn't leave those areas.

And Somalia has been a mess since around 1990. Just watch "Black Hawk Down" or more recently "Captain Phillips" to understand better the problems of Somalia.

And you can just extrapolate the problems from these two movies into Northern Syria, Northern Iraq, Yemen and more of the same for Somalia if you want to see what is likely to happen there the next 10 to 30 years. However, it is my belief that at some point Saudi Arabia will come in force into Yemen to reinstall a Sunni government there compatible with their government in Saudi Arabia.