As Muslims moved in to certain areas, they appeared as settlers. Traveling nomads in search of a place to live. As the population of Muslims grew in those areas they began to ask or demand more things of the local populace and the ruling government. Usually, once a Muslim density of 10% is achieved, they start demanding Sharia Law be enacted, and shortly thereafter, open conflict usually erupts. This is happening all over Africa right now, and could be forthcoming in the Netherlands as well.
To be honest, I am not worried about Sharia Law becoming a reality in the United States; and in fact I can almost guarantee that should such a coup be tried, the amount of blood that would flow through the streets would be epic. People are still uneasy about Muslims almost a decade after 9/11. With at least 3 failed attempts in th last few years by Muslim extremists inside the United States, people still feel wary of Islam.
Should it come to outright conflict, with one group demanding that the very freedoms Americans fought and died for be replaced with an antiquated and barbaric form of totalitarian government, those usurpers will be promptly eliminated, buried in mass graves, and a giant celebration would be thrown afterward. That is how America rolls, you got a problem with that?