🔎 The Puzzle

Alliances are normally seen as public commitments meant to deter attacks by signaling an ally's willingness to defend a protégé. Secret alliances are puzzling under that logic because, being hidden, they cannot deter through public signaling.

🧩 Core Argument

• Alliances do two things: signal commitment to a protégé and signal the members' intentions more broadly.
• A newly formed alliance can signal to a shared enemy that the members' interests are not aligned with the enemy's—potentially provoking the enemy into war rather than deterring it.
• Because an alliance can thus undermine deterrence by changing perceived intentions, states sometimes prefer to keep alliance agreements secret.

📐 Model and Research Design

• A formal game-theoretic model is analyzed in which states can form either secret or public alliance agreements.
• The model explicitly compares the signaling and deterrent consequences of secret versus public alliances.

📌 Key Findings

• Secret alliances cannot deter through public signaling, which explains the puzzle of why secrecy might be chosen.
• The possibility of secret alliances has broad effects on deterrence dynamics: the mere option to form hidden pacts can weaken the deterrent value of existing public alliances.
• In some strategic environments, states deliberately hide alliances to avoid provoking a shared enemy; in others, the existence of secret pacts can unintentionally reduce overall stability.

⚙️ Why It Matters

These results challenge a simple signaling view of alliances by showing that alliance formation can both deter and provoke. The availability of secret alliances changes the logic of deterrence and may reduce the protective value of public commitments.