S0020818321000114jra 164..203

Cooperation among militant organizations contributes to capability but also presents security risks. This is particularly the case when organizations face substantial repression from the state. As a consequence, for cooperation to emerge and persist when it is most valuable, militant groups must have means of committing to cooperation even when the incentives to defect are high. We posit that shared ideology plays this role by providing community monitoring, authority structures, trust, and transnational networks. We test this theory using new, expansive, time-series data on relationships between militant organizations from 1950 to 2016, which we introduce here. We find that when groups share an ideology, and especially a religion, they are more likely to sustain material cooperation in the face of state repression. These findings contextualize and expand upon research demonstrating that connections between violent nonstate actors strongly shape their tactical and strategic behavior. Alliances among militant organizations have long been a matter of both academic and policy concern. Nearly twenty years ago, the 2003 US National Strategy for Combating Terrorism stated that “the interconnected nature of terrorist organizations necessitates that we . . . ensure that all linkages between the strong and the weak organizations are broken, leaving each of them isolated, exposed, and vulnerable to defeat.”1 Breaking down the relationships among militant organizations remains a priority. For example, the UN’s Analytical Support and Sanctions Monitoring Team recently noted that securing peace in Afghanistan will hinge on degrading cooperation between the Taliban and al-Qaeda (AQ).2 Despite the priority placed on disrupting militant relationships, researchers know little about why some are more durable than others. While it is well established that shared ideology facilitates the initiation of cooperation,3 we contend that it also enhances the durability of that cooperation. By generating reputational incentives and engaging external networks of co-ideologues who can help monitor and 1. Government of the United States 2003. 2. Analytical Support and Sanctions Monitoring Team 2020. 3. Bapat and Bond 2012; Horowitz and Potter 2014. International Organization 76, Winter 2022, pp. 164–203 © The IO Foundation 2021 doi:10.1017/S0020818321000114 h t t p s : / / d o i . o r g / 1 0 . 1 0 1 7 / S 0 0 2 0 8 1 8 3 2 1 0 0 0 1 1 4 D o w n l o a d e d f r o m h t t p s : / / w w w . c a m b r i d g e . o r g / c o r e . I P a d d r e s s : 3 5 . 1 6 0 . 2 7 . 2 2 1 , o n 2 4 A p r 2 0 2 2 a t 1 5 : 4 6 : 0 5 , s u b j e c t t o t h e C a m b r i d g e C o r e t e r m s o f u s e , a v a i l a b l e a t h t t p s : / / w w w . c a m b r i d g e . o r g / c o r e / t e r m s .