“surprise military strike conducted by the Japanese navy against the United States’ naval base at Pearl Harbor, Hawaii on the morning of Sunday, December 7, 1941, later resulting in the United States becoming militarily involved in World War II.” source: Wikipedia

The objective of the attack was to prevent the U.S. from interfering with further Japanese conquests of Pacific colonies.  Almost 2,500 people were killed that day (most of them military), the attack occurred through two waves via air and water, and U.S. President Frankin D. Roosevelt’s historical quote was calling the surprise attack “a date which will live in infamy.”

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National Geographic (informative maps and timelines)

Wikipedia