Terrorism in its purest form is self-help by organized civilians who covertly inflict mass violence on other civilians. Pure sociology explains terrorism with its social geometry—its multidimensional location and direction in social space. Here I build on the work of Senechal de la Roche (1996) and propose the following geometrical model: Pure terrorism arises intercollectively and upwardly across long distances in multidimensional space. Yet because social distance historically corresponded to physical distance, terrorism often lacked the physical geometry necessary for its occurrence: physical closeness to civilians socially distant enough to attract terrorism. New technology has made physical distance increasingly irrelevant, however, and terrorism has proliferated. But technology also shrinks the social universe and sows the seeds of terrorism's destruction.