The results of this study show that more than 96 percent of more than 16,000 terrorist attacks were in fact directed at non-United States targets. Not only did groups considered to be threatening rarely attack the United States, but more than 90 percent of these groups' non-United States attacks were domestic. Most groups operated primarily at home against local targets. However, the attack trajectories for United States and non-United States attacks showed considerable similarity. In both cases, it was found that four trajectories best explained the attack patterns from 1970 to 2004. Three "waves" of terrorist attacks with relatively sharp ascents and declines were identified, and a fourth and largest trajectory of groups that struck for only a short period of time or infrequently. An interpretation of these results was that the activities of approximately half of the groups analyzed did not fit neatly into clear terrorism waves. The overall results show that most terrorist attacks by foreign groups deemed dangerous to national security by the United States Government were in fact directed at non-United States targets. Although researchers began to assemble open-source terrorism event databases in the late 1960s, until recently most of these databases excluded domestic attacks. Based on a newly available event database composed of domestic and transnational terrorist attacks, this study examined the anti-United States and non-United States attack patterns by organizations identified as dangerous for the United States. It examined 16,916 attacks attributed to 53 foreign terrorist groups between 1970 and 2004. Tables, figures, and references