Final answer:
December 7, 1941 is important because it is the date of the attack on Pearl Harbor, which led to the US joining World War II.
Step-by-step explanation:
December 7, 1941 is an important date in History because it marks the attack on Pearl Harbor by Japan, which led to the United States' entry into World War II. Following the attack, the United States declared war on Japan and Germany. This event had a significant impact on the course of the war and ultimately shaped the outcome of World War II.
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