Mostly due to the social environment and the population at the time constrained.

Then just experienced the First World War, look at the different results of the three countries:

Germany, the defeated country, lost the war and had to accept the Treaty of Versailles (you can check it out), coupled with the impact of the economic crisis, the people's lives are even more unprotected, and the root cause of all of this is thought to be due to the loss of the war caused by the war, the only way to win a war to reclaim The only way to get it back was to win a war (Bismarck's politics of irony). Hitler was able to capitalize on this by constantly promoting nationalism in the narrow sense of the word, and thus embarked on the path of fascism.

Though Japan is a victorious country, but looking back on the history of Japan's development, basically it is in the war of betting on the fate of the country to gain profits, such as: Sino-Japanese naval battle, Russo-Japanese War, etc., each war allows Japan to make huge profits, coupled with the encouragement of Bushido, militarism, Japan was hit by the economic crisis to embark on the road of militarization fascism, it is too normal.

And the United States in World War I when the early stage is to remain neutral, and through the sale of arms to the warring parties, supplies, etc., big war money, indirectly, also stimulate the development of American society, development is the hard way, in the crisis by the adoption of the New Deal, the tree to move the people to live, the economy will be restored. The social situation in the U.S. had little interest in the home front war, and making war money was the main thing.

Historical propositions, mutual discussion.