Buck-passing

Buck-passing is a core concept in structural realism, most fully developed by John Mearsheimer in The Tragedy of Great Power Politics (2001). When a great power perceives a rising threat, it has two main options: internal/external balancing (building up its own forces or forming alliances to confront the threat) or buck-passing (letting another state — the "buck-catcher" — absorb the costs of containing or fighting the aggressor). The passer hopes the catcher and the threat will exhaust each other, leaving the passer relatively stronger.

Mearsheimer argues buck-passing is especially attractive in multipolar systems, where multiple potential balancers exist and responsibility is diffuse. In bipolarity, by contrast, there is no one to pass the buck to, so balancing is the default. Geography also matters: states separated from the threat by buffer states or large bodies of water find buck-passing easier.

Classic illustrations cited in the realist literature include:

• Britain and France in the 1930s, each hoping the other (and later the Soviet Union) would bear the brunt of containing Nazi Germany.
• The Soviet Union's 1939 Molotov–Ribbentrop Pact, which Mearsheimer reads as an attempt to pass the German buck westward.
• The United States before 1917 and before 1941, relying on European and Asian powers to check Imperial Germany and then the Axis.

The strategy carries serious risks. If the buck-catcher is defeated or bandwagons with the threat, the passer faces a far stronger adversary alone. Buck-passing can also produce underbalancing (Randall Schweller, Unanswered Threats, 2006), where collective failure to confront a revisionist power allows it to grow unchecked.

Buck-passing is often contrasted with chain-ganging, the opposite multipolar pathology in which alliance commitments drag states into unwanted wars, as in 1914.