Final answer:
Japan's attack on Pearl Harbor was a surprise because diplomatic negotiations were ongoing for peace in the Pacific. The attack caught the United States off guard, leading to their entry into World War II.
Step-by-step explanation:
President Roosevelt considered Japan's attack on Pearl Harbor as a surprise because Japan and the United States were engaged in diplomatic negotiations to solidify peace in the Pacific. There had been no direct indication that Japan was planning a military attack on the United States. This surprise attack by Japan caught the United States off guard and led to their entry into World War II.
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