Serious question. Do you really think they would stop killing Americans if we just up and left? Honestly?
Yes, over time. Take out the religious element for a moment and reverse the situation. Imagine America had an occupying foreign power on its soil pitting the regional areas against each other, interfering in elections, killing civilians, and allowing their corporations to reap the profits exploiting native resources. Actually, you don't have to imagine. We had one and fought two wars (1776 & 1812) to throw the bastards out! And we relied heavily on 'terroristic' tactics to do so...including bombs in civilian areas, snipers and guerilla tactics. Once they were defeated and we had our land back we didn't continue to fight the British.
The religious aspect complicates matters because it's used by the local population and leaders to rally support against America (the occupying army). Religious zealotry flourishes in certain conditions. Poverty, hopelessness, and war. The middle east is saturated with all three. America, sadly, acerbates all those situations because our military industrial complex DEPENDS on cheap oil to maintain superiority and project strength around the world. It's the nature of an empire. What we are experiencing is the CIA's definition of 'blowback'. We'll never reduce all violence in the world but you can't ignore the geopolitical influences in its cause. To sit back and jingoistically proclaim 'Islam is evil' as if that's the sole reason for violence is naive...and ultimately a red herring. The elites in the world love to stir up the populations primitive furies to fight wars and have used the differences of religion to do so since the dawn of time.