Looking Back on the Deadliest Terror Attacks in the United States

"Beginning with the attacks of September 11, 2001, the 21st century has seen a marked rise in the threat of terrorism. Since 1970, more than 3,900 people have been killed by terrorist attacks in the United States, and data from the National Consortium for the Study of Terrorism and Responses to Terrorism , or START, shows that 88% of those fatalities occurred since the year 2000."

"While nearly a quarter century has passed since the events of 9/11, terrorism remains a leading threat to American national security. In its 2025 Homeland Threat Assessment report, the U.S. Department of Homeland Security stated that the terrorism threat environment remains high, due to a number of social, political, and ideological factors, as well as international developments. These include U.S. election cycles, grievances toward specific racial, religious, or gender identity groups, and the conflict between Israel and Hamas."

Since 1970 more than 3,900 people have been killed by terrorist attacks in the United States, with 88% of those fatalities occurring since 2000. The terrorism threat environment remains high due to social, political, and ideological factors and international developments, including U.S. election cycles, grievances toward racial, religious, or gender identity groups, and the Israel–Hamas conflict. Potential perpetrators include domestic violent extremists, foreign terrorist organizations, and inspired homegrown violent extremists. Terrorism remains dynamic, lone attackers can still elude federal law enforcement, and the START Global Terrorism Database records incidents used to identify attacks with at least ten fatalities.

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