But the breakdown of extremist ideologies behind those attacks may come as a surprise. Since Sept. 11, 2001, nearly twice as many people have been killed by white supremacists, antigovernment fanatics and other non-Muslim extremists than by radical Muslims: 48 have been killed by extremists who are not Muslim, including the recent mass killing in Charleston, S.C., compared with 26 by self-proclaimed radical Muslims, according to a count by New America, a Washington research center.
In the United States since Sept. 11, terrorist attacks by antigovernment, racist and other non-Muslim extremists have killed nearly twice as many people as those by radical Muslims.
The contentious question of biased perceptions of terrorist threats dates back at least two decades, to the truck bombing that tore apart the federal building in Oklahoma City in April 1995. Some early news media speculation about the attack assumed that it had been carried out by Muslim militants. The arrest of Timothy J. McVeigh, an antigovernment extremist, quickly put an end to such theories.
The bombing, which killed 168 people, including 19 children, remains the second-deadliest terrorist attack in American history, though its toll was dwarfed by the roughly 3,000 killed on Sept 11.
“If there’s one lesson we seem to have forgotten 20 years after Oklahoma City, it’s that extremist violence comes in all shapes and sizes,” said Dr. Horgan, the University of Massachusetts scholar. “And very often, it comes from someplace you’re least suspecting.”
Fort Hood shooting
Boston Marathon bombing