Tectonic Boundaries and Strongholds: The Religious Geography of Violence in Northern Ireland

The conflict in Northern Ireland was an example of "complex warfare" with both insurgency and sectarian violence. We present a unified model that helps to identify these two forms of conflict from the spatial distribution of violence. The model predicts that tectonic boundaries between residential areas of opposed groups drive sectarian violence. Violence between the minority and state forces takes place in minority strongholds. We test the model with fine-grained data on religious composition and geo-referenced data on killings with detailed information on attackers and targets. We also show that sectarian violence can predict the placement of barriers (i.e. so-called "peace lines"). Finally, we analyze the effect of a troop surge in 1972 and the proximity to the Republic of Ireland on the two elements of the conflict.