The RAND Database of Worldwide Terrorism Incidents (RDWTI) contains data on terrorist incidents worldwide from 1968 through 2009. Terrorism is defined as the deliberate creation and exploitation of fear through violence or the threat of violence in the pursuit of political change.
According to the Rand database, there were 567 terrorist incidents in the United States between 1968 and 2009. The most terrorist incidents, 140 out of 567 or 25% of the total during this period, were due to one group or cause, anti-Castro Cubans. The anti-Castro terrorist groups have killed 6 people, mostly advocates of dialogue with Cuba such as Eulalio Jose Negrin who was gunned down in 1979. Numerous bombings have also been traced to these groups including hotel bombings in Miami, bombings in New York of consulates (also Madison Square Gardens) and near-miss airplane bombings. Connections between anti-Castro groups, the CIA and the Bush dynasty remain controversial.
The group responsible for the second highest number of terrorist incidents on US soil, 62 incidents or 10% of the total (1968-2009), is the Jewish Defense League. Mostly these have been bombings in New York City of places or people attached to the Soviets. Perhaps the best known is the 1986 tear-gassing of the Metropolitan Opera House on the visit of the Moiseyev Dance Company. Rand tallies 2 deaths in total to the JDL.
Although these groups committed many terrorist acts on US soil neither had much interest in terrorizing US citizens per se, perhaps explaining the relatively low body counts in the United States.