According to a chronology of international terrorist incidents compiled at the Rand Corporation, the United States led the list of 10 countries by suffering 144 out of 1,166 incidents that occurred between 1968 and 1978. In another chronology that recorded 5,529 domestic terrorism incidents for 10 countries, the United States places third, with 583 incidents. The impression of U.S. immunity to terrorist violence exists, however, not only because of the way we perceive the severity of terrorism, but also because the high level of violent crime overshadows the comparatively low level of political violence. In addition, ethnic-based separatist movements which might give rise to terrorist acts or particular ideological movements such as Marxism or Fascism have not been powerful forces in American history. The United States has experienced little terrorism from abroad because most terrorist groups operate close to home, with the exception of Palestinian groups, which prefer to operate in Western Europe. Bombings represented about 84 percent of all U.S. terrorist incidents. A handful of groups accounted for the 356 bombings and other terrorist actions that occurred between 1970 and 1978. These included the Weather Underground, the New World Liberation Front, various anti-Castro Cuban organizations, Puerto Rican separatists, the Jewish Defense League and its successors, and the Klu Klux Klan. No major terrorist threat currently appears to exist in the United States, with the possible exception of terrorist violence on behalf of Puerto Rican independence. Politically motivated violence probably will persist in the United States, however, at least at the levels seen during the last decade.