Yesterday was the 16th anniversary of the 9/11 attacks. Those attacks murdered 2,983 innocent people and remain the deadliest in world history by a factor of anywhere from 6.4 to 9.1 (many disagree whether the 1978 Cinema Rex fire in Iran that killed 470 people was terrorism). All of the 19 hijackers were foreign-born, 15 from Saudi Arabia, 2 from the United Arab Emirates, and one each from Lebanon and Egypt. They all entered lawfully, 18 on tourist visas and 1 on a student visa.
Many folks prophesied a new world of near constant destructive terrorist attacks on U.S. soil that would frequently rival 9/11. These predictions were repeated so frequently that a version of the phrase "a post 9/11 world" became clichéd. That vision of a terrible future never happened.
Remarkably, the chance of dying in a terrorist attack after 9/11, no matter the origin of the attacker, was actually lower in the post 9/11 world of 2002-2016 than it was in the pre-9/11 world (14 years before the attacks). After 9/11, the annual chance of being murdered in an attack on U.S. soil committed by any terrorist was about 1 in 26.4 million per year – far lower than the 1 in 16.9 million per year prior to 9/11. The chance of being murdered by U.S. born terrorists in a domestic attack also decreased after 9/11 as it fell from about 1 in 18.1 million a year to 1 in 37.9 million per year (Table 1).
Foreign-born terrorists murdered 26 people on U.S. soil since 9/11 through the end of 2016, meaning the chance of being murdered in one of those attacks was about 1 in 176.6 million per year. That is more than double the 12 who were murdered by foreign-born terrorists on U.S. soil in the 14 years prior to 2001. In those 14 years prior to 9/11, the chance of being murdered in a terrorist attack committed by a foreign-born attacker was about 1 in 302.3 million per year.
Table 1 - Annual Chance of Being Murdered in a Terrorist Attack by the Attacker's Country of Origin and Time Period
Source: Author's expansion of "Terrorism and Immigration: A Risk Analysis."
Obviously, a calculation of the terrorism risk over this entire time should include the murders committed by the 19 hijackers on 9/11, as I do here, here, and elsewhere. But the claim that the post-9/11 world is more deadly because those attacks jolted us into a new and more brutal terror equilibrium is simply not true (at least when considering domestic terrorism).
This post 9/11 safety effect could theoretically be the dividends of increased government anti-terror measures, though this is highly unlikely given this superb research on the lack of cost-benefit calculations in the allocation of anti-terrorism funding by experts John Mueller and Mark G. Stewart. The best explanation is that deadly terrorist attacks are rare because not many people are interested in killing strangers, most people who are interested in murdering strangers are incompetent, and many things have to happen for a terrorist attack to be successful – all while being chased by anti-terrorism police. These four reasons, by themselves, explain why the risk is so small. We should all be thankful for that.