Is war the rational and well-calculated pursuit of states, or are decisions for war more
often dominated by miscalculation and misperception? This is an important question because
assumptions about the extent of rationality in decisions for war underlie policy debates on a range
of subjects from deterrence and missile defense to peacekeeping. Arguments about rationality
also underlie academic debates about the general causes of war and the methodologies to study
them, as well as historical debates about the causes of specific wars.
If one assumes that states start wars intending to win them, then losses by war initiators
will tend to indicate that the decision for war was dominated by miscalculation and misperception.
This assumption means that the extent of miscalculation and misperception can be measured by
looking at the win and loss rates of initiators.
Using the Correlates of War (COW), Militarized Interstate Dispute (MID), and National
Material Capabilities (NMC) databases, and we find that initiators won 55% of the seventy-nine
large interstate wars between 1815 and 1991. The utility of war has declined markedly over time.
In the forty-seven wars since 1900, the success rate declined to 43%. Since 1945, initiators won
33% of twenty-three wars. Despite declining win rates, states initiate wars at an increasing to
steady (since 1920) rate over time. States are not learning that war increasingly does not pay.
Declining win rates and steady initiation rates provide the main basis for our core
argument: miscalculation and misperception are increasing. This argument is bolstered by other
findings showing that, for example, relative power is often not a good predictor of outcomes.
These findings have impacts across a range of policy and academic debates. If
miscalculation and misperception is increasing, then deterrence is getting harder. The utility of
rationalist approaches to the causes of war is decreasing. Causes of miscalculation and
misperception deserve more study.
2
Convention