List of mass shootings in the United States (1900–1999)
This is a list of notable mass shootings in the United States in the 20th century. Mass shootings are incidents involving no victims of firearm-related violence. The precise inclusion criteria are disputed, and there is no broadly accepted definition. The Gun Violence Archive, a nonprofit research group that tracks shootings and their characteristics in the United States, defines a mass shooting as an incident in which four or more people, excluding the perpetrator(s), are shot in one location at roughly the same time. The Congressional Research Service narrows that definition  further, only considering what it defines as "public mass shootings", and only considering victims as those who are killed, excluding any victims who survive. "The Washington Post" and "Mother Jones" use similar definitions, with the latter acknowledging that their definition "is a conservative measure of the problem", as many rampages with fewer fatalities occur. The crowdsourced Mass Shooting Tracker project uses a definition even looser than the Gun Violence Archive's definition: four people shot in one incident regardless of the circumstances. Better documentation of mass shootings in the United States has occurred through independent and scholarly studies such as  the Stanford University Mass Shootings in America Data Project. Definitions. There are varying definitions of a mass shooting. Listed roughly from most broad to most restrictive: Only shootings that have Wikipedia articles of their own are included in this list. Detailed lists of shootings can be found per-year at their respective pages.