The short answer is that these countries were each in the grip of a fantatical type of "nationalism," perhaps for essentially the same reasons.
The more thorough answer to this question needs to recognize various social and economic factors that were all coming together in the post-World War I years. But these factors were intricately connected with the ethnic chauvinism of these states. Any discussion of nationalism will inevitably refer to the economies and social structures as they existed, and changed, in Italy, Germany, and Japan at that time.
Of all the large countries in Europe, Italy and Germany were the most recent ones to have formed unified nation-states, in 1870–71. For centuries, both had been a patchwork of basically independent, and often foreign-dominated, principalities. Both the Germans and Italians had a sense of past, and partly mythic, greatness which they felt had been denied to them either by their own backward rulers or by the other European powers who were seen...
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