Terrorism is a hazard to human life and material prosperity that should be addressed in a sensible manner whereby the benefits of actions taken to contain it outweigh the costs. Foreign-born terrorists were responsible for 86 percent (or 3,037) of the 3,518 murders caused by terrorists on U.S. soil from 1975 through the end of 2017. Of the other 481 murder victims of terrorists, 413 were murdered by native-born Americans, and 68 were murdered by unidentified terrorists. This paper is an update and expansion of a previous Cato policy analysis of the risk of foreign-born terrorists by the visa categories they used to enter the United States. This updated policy analysis also includes native-born terrorists in a separate category, estimates of injuries sustained in terrorist attacks, the terrorist countries of origin, and terrorist ideologies. This version also corrects minor errors such as the exclusion of some nondeadly foreign-born terrorists and changes in their visa statuses before 1990.
Including those murdered in the terrorist attacks of September 11, 2001 (9/11), the chance of a person perishing in a terrorist attack on U.S. soil committed by a foreigner over the 43-year period studied here is 1 in 3.8 million per year. The hazard posed by foreigners who entered on different visa categories varies considerably. For instance, the chance of an American being murdered in a terrorist attack by a refugee is about 1 in 3.86 billion per year, while the annual chance of being murdered in an attack committed by an illegal immigrant is zero. By contrast, the chance of being murdered by a tourist on a B visa, the most common tourist visa, is about 1 in 4.1 million per year. Compared to foreign-born terrorists, the chance of being murdered by a native-born terrorist is about 1 in 28 million per year.
There were 192 foreign-born terrorists who planned, attempted, or carried out attacks on U.S. soil from 1975 through 2017. Of those, 65 percent were Islamists, 18 percent were foreign nationalists, 6 percent were right-wingers, 6 percent were non-Islamic religious terrorists, 3 percent were left-wingers, and the rest were separatists or adherents of other or unknown ideologies. By comparison, there were 788 native-born terrorists who planned, attempted, or carried out attacks on U.S. soil from 1975 through 2017. Of those, 24 percent were right-wingers, 22 percent were white supremacists, 16 percent were left-wingers, 14 percent were Islamists, 11 percent were anti-abortion, and 6 percent were others. This expanded terrorism risk analysis can aid in the efficient allocation of scarce government-security resources to best counter the small terrorist threat.
