In the United States, the years since 9/11 have been a period of heightened awareness about the threat of terrorism, but they haven’t been a period of frequent attacks. The U.S. witnessed a much higher number of terrorist attacks in the 1970s than in the 2000s. But the destruction of the World Trade Center and a piece of the Pentagon was something unprecedented; no single terrorist attack in history up to that point had killed so many. The pipe bombings of the 1970s—when, as Marquette University’s Risa Brooks has written, “the country experienced a rash of bombings by Puerto Rican nationalist groups and the militant left, such as the Weather Underground, which combined were responsible for more than 100 bombings”—were low-casualty affairs that, if they killed anyone, tended to do so one or two people at a time.
At the time, the subject of “terrorism” didn’t attract much scholarly attention. Martha Crenshaw was one of the pioneers of terrorism studies and, incidentally, my advisor in graduate school. In the decades since she started researching it, terrorism has gone from a largely ignored subfield to an object of serious, and some might say excessive, concern among policymakers and the public. There are hundreds of ways to define “terrorism,” and they tend to involve violence committed by a non-state actor to achieve some kind of political objective. (Though, to complicate matters further, there is also the notion of “state terror” or “terror from above,” involving politically motivated violence by governments to oppress or intimidate domestic opponents.)
Read more: The Atlantic