The organization must be foreign. A dissident is an exile from their own country who plots and plans the overthrow of the regime in power. An insurrectionist is a person in armed opposition to the laws of the United States. There are a number of groups in the United States who regularly resort to violence in the furtherance of their political goals, or who reject with armed force the authority of the U.S. government. Such groups attack families, clinics, and offices, frequently using arson or bombing.
Leftist groups tend to operate under several different names.
Rightist groups tend to have the most members. Someone can belong to several different groups. Islamic Media Ethnic Conflict by Vincent Ferraro, Mount Holyoke College Minorities at Risk Project Tracking the status and condition of ethnopolitical groups around the globe.