The US made several policy changes to combat terrorism following the 9/11 attacks. Most notably, it created the Department of Homeland Security, increased airport security, and went to war in Afghanistan.
In the two decades since the attack, there were far fewer terrorist acts on US soil and most attacks aren’t lethal, according to data from the National Consortium for the Study of Terrorism and Responses to Terrorism (START). The consortium is a Department of Homeland Security science and technology center.
While the 9/11 attack was committed by terrorists associated with the extremist Al Qaeda group, most terror incidents in the US are conducted without a connection to a formal organization and are motivated by a wide range of ideologies.
An FBI definition based on federal statute describes terrorism as “violent, criminal acts committed by individuals and/or groups who are inspired by, or associated with, designated... terrorist organizations or nations.” A country or nation can be a state sponsor of terrorism if the Secretary of State determines the country repeatedly provided support for terrorist acts. The US currently considers four countries as state sponsors of terrorism: Syria, Iran, North Korea, and Cuba. North Korea and Cuba were the most recent additions to that list, added in 2017 and this past January, respectively.
Similarly, an FBI definition of domestic terrorism describes it as “violent, criminal acts committed by individuals or groups to further ideological goals stemming from domestic influences, such as those of a political, religious, social, racial, or environmental nature.”
The 9/11 attacks killed 2,908 people between the plane strikes at the World Trade Center in New York City, the Pentagon in Washington, DC, and the crash of Flight 93 in Shanksville, Penn. Since those attacks, 549 Americans have died in terrorist attacks, according to an analysis of the Global Terrorism Database, maintained by START. In 2019, the most recent year for which data is available, 51 people died in terrorist attacks in the US.
About a quarter of all terrorist attacks in the US from 2015 to 2019 involved firearms. Those firearm incidents were responsible for almost all terrorism-related deaths at that time.
More than 106,000 terrorist attacks have occurred worldwide since 9/11, according to the Global Terrorism Database. The number of terrorism attacks has decreased steadily since the 2014 peak of about 13,500. Around 6,700 attacks occurred worldwide in 2019. About one fifth of terrorist attacks that year occurred in Afghanistan in 2019.
Since 2001, there have been 546 terrorism attacks on US soil. The number of terrorism attacks in the US have risen from 20 in 2013 to as high as 73 in 2018. The nation has averaged about 30 terrorism attacks a year from 2002 to 2019. Most terrorism attacks in the US do not result in deaths, except for the deaths of terrorists, according to a START report. Eighty-four percent of the 64 US terrorist attacks in 2019 were not lethal.
While the 9/11 attacks were committed by terrorists with an extremist Islamic ideology, subsequent terrorist acts in the US have had a wide range of origins. In 2019, attacks in the US were committed by attackers with “antifascist, anti-government, anti-LGBT, anti-Muslim, anti-Semitic, anti-white, left-wing, pro-choice, and white supremacist/nationalist extremism” ideologies, among others, according to a 2020 START report. Attackers typically did not have ties to organized, formal groups like al Qaeda.
The National Consortium for the Study of Terrorism and Responses to Terrorism (START) is a Department of Homeland Security Science and Technology Directorate (DHS S&T) Emeritus Center of Excellence (COE) headquartered at the University of Maryland.
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