We evaluate the argument that Islamist terrorist attacks represent a distinctive "4th wave" of transnational terrorism that has supplanted Leftist terrorism. Drawing on ITERATE data for 1968-2003, the annual count of Leftist attacks has declined since the end of the Cold War while Islamist attacks have persisted and spiked upward in 2002-03. Pooled cross-sectional time-series regression demonstrates that the generation of Islamist terrorism is more deeply rooted in the social strains created by modernization, the competition between Islam and other religions, and the growth of secular government. Leftist terrorism was uniquely stimulated by Cold War rivalry (and subsequently declined thereafter). Both forms of transnational terrorism display a kindred nature, however, in that both are encouraged by the social strains of transitional development and the political opportunities created by increasing political rights. Moreover, foreign direct investment is associated with reduced transnational terrorism over time, calling into question theories that stress global order and anti-systemic violence against international capitalism.