The similarities in structures and dynamics between Fascist Italy and Nazi Germany provide few clues to help explain the enormous disparities between them in expansionist zeal, fighting power, and staying power. Both regimes arose from compromises between militant nationalist mass parties born of the Great War and establishments that same war had shaken and humiliated. For both, war was an instrument not merely of external conquest but also for the barbarization of their societies and the final taming or destruction of all institutions, from churches to officer corps to the Italian monarchy, that blocked their paths to total power at home. Fascist and Nazi expansion was the polar opposite of “social imperialism,” the preservation or restoration of the political and social order at home through success abroad. The wars of Fascism and Nazism, far from aiming to avert revolution, were designed to make it.

Yet one dictatorship crumbled almost apologetically. The other defended to the last cartridge an empire that at its height stretched from the North Cape to the Western Desert and from the Pyrenees to the Caucasus. Understanding that difference in outcome requires an attempt to separate the layers of causation involved. The most important factors appear to fall into three roughly chronological categories: underlying or inherited structures and forces, structures and forces connected with the regimes themselves, and events and their sequence.