How can defense alliances capture efficiency gains when coordination and opportunism costs are high? Specializing within a collective offers economic and functional benefits, but states still must bargain over how those gains are distributed and keep collective-action costs from eroding cooperation. The central argument is that alliances combining high strategic compatibility with clear hierarchy minimize these problems by distributing defense capabilities efficiently and encouraging complementarity rather than redundancy.

🔎 Measuring Division of Labor Across Militaries

• Introduces a novel network-level measure of division of labor designed to capture how defense capabilities are distributed and specialized across alliance members.
• Applies this measure to national military capabilities data covering 1970–2014.

🔑 Key Findings

• Alliances characterized by high strategic compatibility and hierarchical structure reduce opportunism and coordination costs.
• Such configurations promote complementarity in capabilities instead of redundancy, yielding more efficient cooperation.
• These efficiency gains are especially important when coordination and opportunism costs are elevated.

🌍 Why It Matters

• Enhances understanding of how modern international security arrangements work in practice.
• Underscores the importance of strategic fit and hierarchy for intra-alliance bargaining and the practical division of defense responsibilities.