Between 1993 and 2001 , the major attacks or attempts against U.S. interests stemmed from militant Islamic jihad extremism except for the 1995 Oklahoma City bombing . On September 11 , 2001 , nearly 3,000 people were killed in New York City , Washington , DC , and Stonycreek Township near Shanksville , Pennsylvania , during the September 11 attacks organized by 19 al-Qaeda members and largely perpetrated by Saudi nationals , sparking the War on Terror . Former CIA Director Michael Hayden considers homegrown terrorism to be the most dangerous threat and concern faced by American citizens today . As of July 2011 , there have been 52 homegrown jihadist extremist plots or attacks in the United States since the September 11 attacks
September 11 attacks
September 11 attacks
Islamic terrorism