Douglas MacArthur's “The Japanese at 12” (1951)

Well, the German problem is a completely and entirely different one from the Japanese problem. The German people were a mature race.

If the Anglo-Saxon was say 45 years of age in his development, in the sciences, the arts, divinity, culture, the Germans were quite as mature. The Japanese, however, in spite of their antiquity measured by time, were in a very tuitionary condition. Measured by the standards of modern civilization, they would be like a boy of twelve as compared with our development of 45 years.

Like any tuitionary period, they were susceptible to following new models, new ideas. You can implant basic concepts there. They were still close enough to origin to be elastic and acceptable to new concepts.

The German was quite as mature as we were. Whatever the German did in dereliction of the standards of modern morality, the international standards, he did deliberately. He didn’t do it because of a lack of knowledge of the world. He didn’t do it because he stumbled into it to some extent as the Japanese did. He did it as a considered policy in which he believed in his own military might, in which he believed that its application would be a shortcut to the power and economic domination that he desired …

But the Japanese were entirely different. There is no similarity. One of the great mistakes that was made was to try to apply the same policies which were so successful in Japan to Germany, where they were not quite so successful, to say the least. They were working on a different level.

Senate Committees on Armed Services and Foreign Relations　(1951), p. 312

※以下のサイトを参照。
１）マッカーサー証言「日本人12歳」の真意： 井沢元彦『「言霊」解体新書』 | Misunderstandings can go both ways
２）Douglas MacArthur | kushima.org