Time Magazine explains some reasons why (besides support for Israel and war on Iraq) there has been more terrorist activity in Britain than here in America. Why are British young Muslims more violent than American young Muslims?
Well among other things, American Muslims are, overall a smaller and better integrated part of the nation's population than anywhere in Europe, tending to be better educated and better off financially than the majority of Americans. In Great Britain and even more in other European nations, Moslems tend to be poor and live in enclaves. I tend to put a lot of stock in this first explanation, myself. There's nothing like few prospects of a good life to interest people in desperate measures, something that our society should be taking seriously as we move further and faster into this "winner take all' economy.
Another factor in "Muslim America" is that Muslims here tend to come from many nations and are, as someone commented yesterday, of different races, and include our homegrown Black Muslim brand. All that Moslem diversity makes it more likely that isolated groups will assimilate into the mainstream rather than clump with other Moslems.
Another factor Time mentions is that in Europe, religiousness of any kind is viewed with disdain, as a threat to secular values. Moslems there feel pervasively misunderstood and sneered at for what is most precious to them, their faith. Here in America, we have our disagreements about faith, but we're accustomed to a larger public square of tolerance about the issue, and Moslem faithfulness fits in better.
Sometimes Americans, especially those whose own values are secular, assume that their way is the peaceful way and "religion causes so much violence in the world." While there's no doubt that religion is one source of violence, it seems likely that appreciative tolerance of the variety of human religiousness has a calming effect.