Mission Impossible: Measuring the Offense-Defense Balance with Military Net Assessment

Charles Glaser’s Rational Theory of International Politics argues that state security competition is not an inevitable consequence of international anarchy.1 To be sure, sometimes the attempt by one state to increase its security has the unintended and unavoidable effect of decreasing the security of others—triggering a spiral of arms racing and diplomatic hostility that results in war. At other times, however, this security dilemma can be avoided. According to Glaser, under a surprisingly wide range of conditions, states should be able to feel secure, build military forces to signal peaceful intentions, and thereby avoid unnecessary competition and conflict. In short, much of the tragedy of international politics could be ameliorated if state leaders were more attuned to conditions conducive to cooperation. What are these conditions? For Glaser, offense-defense variables are key. The nature of the offense-defense balance (ODB), and whether offense and defense are distinguishable, helps determine whether states can avoid negative security spirals. When the ODB favors defense, and the forces that support offense are distinguishable from the forces that support defense, securityseeking states can build defensive forces at less risk and without threatening the adversary’s ability to defend itself. This reassuring defense posture signals benign motives, encourages cooperative arms control policies, and has the potential to improve political relations over time. In sum, offense-defense variables are a crucial determinant of a state’s security environment and vital to the causal logic and policy prescriptions of Glaser’s theory.