Combining data from a newly created global terrorism database and a chronological index of deaths from the conflict in Northern Ireland, I evaluate 3,328 terrorist attacks perpetrated by Northern Irish groups between 1969 and 1992. I assess whether responses to terrorism increase or decrease subsequent terrorist activity using two competing theoretical perspectives. While rational choice theories assume that government intervention decreases terrorism by increasing the costs of crime, legitimacy theories suggest retaliation may increase terrorism by decreasing the legitimacy of the government. Using Cox proportional hazard models, I estimate the impact of six government interventions on the hazard of a terrorist attack. My results provide minimal support for rational choice theories but ample support for theories of legitimacy. In five of the six cases examined, government intervention resulted in increased activity for at least one terrorist group. Overall, my results support the conclusion that military-oriented counter terrorism may be counterproductive.