And then when the country's all Muslim, they start killing each other. Christians has been through this but at a time when WMDs are not available yet and Christian sects have all eventually reformed.
There are a few 100% Muslim countries around the world, such as Afghanistan, Saudi Arabia, Yemen, Sudan.etc. All these countries are currently affected by civil war, perhaps with the exception of Saudi Arabia.
Saudi don't yet have a civil war because they are the ones spreading radicalism. They donate a mosque to your area and you know what's coming next. They've had a few attacks though but those are mostly targeted against the Shia minority there.
Like many gulf states, they were also quite good at stuffing their people's mouths with oil money to placate them. If that fails, then you go to jail, it's not like anyone or the international community would do anything. Everyone, even America, just turn a blind eye.
All turn a blind eye only because they depend on oil. Now go to the global trends that demand for oil will fall and the price of black gold will decline accordingly. The Americans have caught these trends, and probably is linked to the decision by Trump to sell us oil. Then maybe the conversation will be different.