The nightclub in Orlando where the worst mass shooting in U.S. history took placeKevin Kolczynski / Reuters

As of Monday morning, the death toll of Sunday’s massacre at an Orlando nightclub stood at 50 including the assailant, making the attack not only the worst mass shooting in U.S. history, but also the deadliest terrorist attack in the United States since September 11, 2001. The toll was more than triple that of the next-deadliest terrorist attack in the United States since 9/11, the San Bernardino shooting of December 2015, in which 14 people were killed. And the weapons used in Orlando, as in San Bernardino, were guns.  

Firearms have a long but not straightforward history in terrorist attacks in the United States and around the world. In 2012, The New Yorker’s Jill Lepore reported that “The United States is the country with the highest rate of civilian gun ownership in the world,” with Yemen ranking a distant second. Yet according to an analysis of the University of Maryland’s Global Terrorism Database (GTD), a comprehensive dataset on more than 140,000 terrorist attacks worldwide since 1970, guns appear less frequently as the primary weapon in terrorist attacks in the United States than in those committed elsewhere in the world.


Weapons Used in Terrorist Attacks in the United States, 1970-2014

 


Weapons Used in Terrorist Attacks Outside the United States, 1970-2014

 


They have, however, been the weapon of choice in more than two-thirds of fatal terrorist attacks in America; for the rest of the world, they were the primary weapon in about half.


Proportion of Fatal Terrorist Attacks in the United States Involving Firearms, 1970-2014


Proportion of Fatal Terrorist Attacks Outside the United States Involving Firearms, 1970-2014

 


Current patterns of terrorism around the world help explain why this is the case. The overwhelming majority of deaths from terrorist attacks occurred in just five countries in 2014, the last year for which the GTD has data—Iraq, Afghanistan, Pakistan, Nigeria, and Syria accounted for nearly 60 percent of all terrorist attacks, and 80 percent of terrorism fatalities, worldwide that year. These are countries in which bombings, including suicide bombings and attacks using improvised-explosive devices, regularly claim dozens of lives at a time. Such weapons are extremely difficult to assemble in the United States, as FiveThirtyEight’s Carl Bialik pointed out on Sunday: “[S]ince Sept. 11, the federal government has monitored the use of explosives and the trade of materials that can be turned into explosives.” 

In terms of fatalities, the Orlando shooting is the third-deadliest terrorist attack in U.S. history. The two deadliest—the September 11 attacks of 2001, which killed some 3,000 people, and the 1995 Oklahoma City bombing, which killed 168—together accounted for 90 percent of terrorism-related fatalities in the United States as of 2014, and did not involve firearms. In general, though, as the GTD’s program manager Erin Miller pointed out last summer, “[d]espite the potential for attacks involving explosives to cause exceptionally high numbers of casualties,” most such attacks in the United States have resulted in no fatalities at all, either because they were intended to destroy property rather than lives, or through simple failure to cause intended casualties. In the United States, she wrote in a report on the use of guns in terrorism, “attacks involving firearms are more likely to be lethal.”

Miller noted that of more than 2,600 incidents of terrorism in the United States between 1970 and 2014, a little over 340, or 13 percent, involved firearms as the primary weapon. (The numbers do not yet reflect last year’s terrorist shootings in San Bernardino and Charleston, nor Sunday’s attack.) Terrorists including ISIS sympathizers may well be able to exploit the ease of obtaining a gun in the United States, but guns’ use in terrorism in America, Miller wrote, “is approximately one-third as common as firearm usage in terrorist attacks in the rest of the world, where 37 percent of attacks involved firearms as the primary weapon.” 

That proportion fluctuates from year to year, however, and in 2014 the proportion of terrorist attacks in America that involved guns spiked, with the U.S. far surpassing the rest of the world in percentage of terrorist attacks involving firearms. It’s worth noting that the number of attacks in the U.S. was low overall that year; of 19 terrorist attacks in the U.S. that year, guns were involved in 14.  


Proportion of Terrorist Attacks Involving Firearms, 1970-2014


It's not yet clear whether this departure from the historical pattern will prove a lasting trend. There are reasons to suspect it could: As security measures put in place following September 11 have made it increasingly difficult to organize terrorist conspiracies on U.S. soil, America has confronted the threat of self-directed “lone wolves,” inspired by but not necessarily connected to larger terrorist organizations like ISIS. Islamic State leaders, like al-Qaeda leaders before them, have purposefully encouraged such attacks, which are difficult to stop, in contrast to complex coordinated attacks, which require the involvement of multiple actors and create more opportunities to draw the attention of law enforcement. Firearms, being simpler to acquire and use independently than the kinds of explosives that can cause mass casualties, seem to fit the tactic. And while there’s a limit to how much damage one individual can cause, America saw on Sunday that the limit is horrifyingly high.

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