This article problematizes the social structure of ethnic groups to account for variation in insurgent mobilization within and across ethnic groups. Relying on network-based approaches to social structure, it argues that insurgent mobilization is constrained by the structural connectivity of the ethnic group, a measure of the extent to which subethnic communities—neighborhoods, villages, clans, and tribes—are socially connected internally and with each other. In agrarian societies, structural connectivity is traced to religion. On the basis of unique data on rebel recruitment from the Mizo insurgency in India and microlevel variations in changes associated with the spread of Christianity among Mizos, the author demonstrates that enhanced structural connectivity resulting from a network of highly centralized churches and institutions under the Welsh Presbyterian Mission significantly bolstered insurgent recruitment. Semistructured interviews of Mizo insurgents and ethnographic evidence from the neighboring Meitei and Naga ethnic insurgencies further support the argument and the casual mechanism.