Rebuilding the foundations of offense-defense theory

The relative ease of attack and defense-the offense-defense balance-is a wi dely used explanatory concept in international politics, playing an importa nt role in literatures ranging from war causation and alliance formation to the determinants of system structure, the importance of relative gains fro m cooperation, or the causes of World War I. Yet the concept of the balance itself remains radically underdeveloped theoretically, clouding the predic tions of the numerous theories that rest upon it and undermining rigorous e mpirical work on the many hypotheses these theories imply. I address this p roblem by presenting and testing a systematic theory of the balance that em phasizes military strategic and tactical choices as its key determinants, b y contrast with orthodox offense-defense theory's focus on technology. This new theory outperforms the orthodox view and has broad implications for in ternational relations theory.