A decade after the Sept. 11 attacks, it increasingly seems to have come to this: Americans have met the enemy - and he is carrying a U.S. passport.
For generations, assimilation has been the story told by the United States - the recipe for making Americans. Irish and Italians, Catholics and blacks, Japanese and Jews joined the mainstream even as they maintained their unique cultures and traditions.
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But today, with the world a mouse click away and most every country in the world accessible in little more than a day, globalization is competing fiercely with assimilation. People who have a foot in two strikingly different cultures no longer leave one behind for the other. Now they can move between them easily, fluidly, quickly.
Thus it becomes possible for a fanatical few Muslim-Americans, living in the belly of what they perceive as a hostile culture, to feel closer to a bombed Afghan village or a Pakistani madrassa than to the America outside their own front doors.
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"There has been a concerted campaign to convince Americans that the radicalization within Islam only happens to people who are impoverished, who are desperate and turn to religion because they don't have any other viable alternative for their life. And we've seen case after case when this simply is not true," says Geneive Abdo, author of "Mecca and Main Street: Muslim Life in America after 9/11."
Shahzad, who was born in Pakistan, fits the profile of many Muslims charged with terrorism in Europe: son of a well-off family, recipient of a graduate degree, married with a comfortable lifestyle.
"Globalization has changed the nature of assimilation," says Abdo, who also is director of the Iran program at the Century Foundation, a progressive think tank. "Other minorities didn't perceive that the United States was at war with them. The Muslims here identify with the Muslims (overseas)."
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That poses no conflict for the vast majority of America's several million Muslim citizens, whose faith has no place for violence or terror. But what, exactly, could push someone from the comparative comfort of the suburbs into attempting a homicidal terrorist attack?
Researchers have found common themes among those who choose violence. Some aspect of their lives has gone off the rails. They are enraged by the deaths of innocents in U.S. war zones. Or they are emboldened by what they see as the creeping immorality of Western society - promiscuity, alcohol, secularism, divorce, single parenthood.
Blind to the faults of Islamic society, they see another side to American freedom, and feel the widespread suspicion of Islam in the United States. And so they want to fight.
"Most Americans don't see this - that every day something happens to underscore the extremely anti-Muslim sentiment in this country," says Muqtedar Khan, a University of Delaware political scientist. "You can't abuse Muslims while you try to assimilate them."
Since 9/11, 146 American Muslims have been publicly accused of planning or carrying out extremist violence, according to Duke University anti-terrorism expert David Schanzer. Most were born in America or were naturalized citizens or legal residents, according to a study that Schanzer co-authored. The largest number of cases occurred in 2009, with a total of 41 suspects.
A separate study found 804 people from around the world charged with terrorism in U.S. federal court since 9/11. Some 273 of them were U.S. citizens, almost triple the amount from any other nation, according to the New York University Center on Law and Security.
Such crimes are enabled by the generation-old web of communication - direct overseas telephone calls, e-mail, live video chats across the ether from continent to continent - that makes winning hearts and minds in a distant locale easier than ever before.
"The radical cleric doesn't have to be in Connecticut to radicalize people in Connecticut," Khan says. "YouTube is the new Afghanistan."
Schanzer said his research indicates that America is less vulnerable to large attacks like the one on the World Trade Center, "but it's possible we are more exposed now to smaller-scale events."
Little things, though, sometimes lead to large consequences. Schanzer cautions against the natural instinct to overreact to small attacks "in a way that changes the character of our country and undermines our ability to project our values across the world."
"The more we distance Muslim-Americans from the mainstream of society and make them feel like outcasts or discriminated against, in some ways we're in a self-perpetuating cycle," he says. "We're increasing the likelihood of individuals from that community being alienated."
So how can we break the cycle? In an increasingly intricate world where multiple cultural identities are everywhere, that's hardly a straightforward question. Because the American dream, always an elusive beast, is more complicated than ever.
"Assimilation is not the answer," Abdo says. "There isn't an answer. The way each Muslim responds to globalized Islam can't be controlled, calculated or predicted."