Answer:
The United States responded with the mobilization of troops, and the declaration of war against Japan, and later Germany & Italy. They also rounded up Issei & Nisei (Japanese-immigrants & Generational Japanese-American) to concentration-like camps, and kept them there mostly to the end of the war. The US then adopted the Europe-First! strategy, in which they would defeat the stronger axis power Germany, before focusing on the defeating Japan.
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