International Terrorism and Domestic Terrorism Trends in the US Post-9/11

• In Event: Modern Terrorism

Abstract

In recent years, several scholars have argued that domestic terrorism is increasing in the United States, while incidents of international terrorism within the US have seemingly subsided. Despite the importance of understanding these trends, there is little empirical evidence with which to assess these trends. The most comprehensive dataset on terrorism, the Global Terrorism Database (GTD), offers some insight into these questions; for example, the GTD shows that between September 12, 2001 and June 30, 2021, there were only 4 terrorism incidents in the United States that were conducted by international terrorist groups such as Al-Qaida in the Arabian Peninsula (AQAP) out of a total of 716 incidents. However, the GTD data does not tell the full story. The database does not distinguish between international and domestic terrorism, and there are large amounts of missing data for incidents where the identity of the perpetrator is unknown. The database does include a variable for classifying the attack as international by defining whether the group crossed a border to commit an attack, but of the 716 incidents in the United States since 9/11, this variable was “unknown” for 619 of the incidents.

This paper will use empirical evidence to analyze the trends in domestic and international terrorism in the post-9/11 period. First, this paper will present a new coding scheme for the 716 terrorism incidents in the US in this time frame, which will classify incidents as domestic terrorism or international terrorism. Second, this paper will expand the methodology from Erik Dahl’s “Plots that Failed” dataset to include failed terrorist plots in this new dataset, which will offer a more comprehensive picture of the threat landscape. Finally, this paper will analyze this new dataset to assess claims about the prevalence of domestic and international terrorism within the US since 9/11. Understanding these trends in terrorism will allow for policymakers to make more informed, data-driven policy decisions in the counterterrorism space.

Author

• Katherine Tucker, Harvard University