Nationalism was a significant force in the way the United States related to Japan during WWII. Not only were the countries at war, but there was also a sense of distrust among many people.
In the case of Japan, due to the fact that the two countries were at war, POWs were kept by the Japanese government. The government did not want to appear inferior, and they also wanted to prove that Japan could be as developed and wealthy as any European power. This excessive pride was a consequence of the nationalism that was encouraged in Japanese politics during these years.
In the case of America, Japanese Americans were displaced and confined even though there was no evidence of their involvement in war activities. The government was afraid of their Japanese legacy, and they believed that if their heritage was Japanese, they were unlikely to be faithful to America. These people were victims of a different type of nationalism, as Americans had a very narrow view of what being an American was.
In WW1, the Japanese army only had to clean up what it could get from the German colonial possessions. Tsingtao was its biggest engagement and went well. It had not cost the lives of countless Japanese soldiers.
Contrast that to WW2, where you have an army that has been fighting in China since 1931 and then was thrust into the jungles of southeast Asia and the Pacific in a bitter fight for survival against the British and Americans. When you have spilled your blood, you are less predisposed to the gallantries of "civilized" fighting.
<span>And then you have the precedent of these exact same foes having turned down Japan's </span>Racial Equality Proposal<span> in 1920. The Japanese understood that the westerners were still looking at them as inferior. That resentment had time to fester in the intervening 20 years, among the ranks of the Japanese army officers.</span>
<span>Last but not least, in the interwar years the entire world saw a slide to totalitarianism, with Japan being no exception
