For years, the U.S. government has been waging counterterrorism campaigns against al-Qaida and other armed groups in safe havens and weak states. What explains the effectiveness of such campaigns? The variation in effectiveness may result from differences in select tactical, organizational, and technological capabilities of the counterterrorism state and its local partner, captured by the concept of the Legibility and Speed-of-Exploitation System (L&S). Empirical studies, including novel fieldwork data, on the U.S. drone war in Pakistan's Waziristan region from 2004 to 2014 reveal the influence of the L&S on targeted groups. From 2004 to 2007, a lack of U.S. counterterrorism capabilities aligning with the L&S allowed both al-Qaida and the Pakistan Taliban to build their operational infrastructure, expand their bases, engage in extensive recruitment drives, and broker important local alliances. In contrast, as the United States made substantial improvements in the L&S from 2008 to 2014, the campaigns against both groups became increasingly effective. Both al-Qaida and the Pakistan Taliban experienced sustained reductions in operational capabilities, losses of bases, and high desertion rates; they also faced growing political challenges, including from within their own organizations. These findings contrast with the view that counterterrorism offers short-term gains at best and is counterproductive at worst.