Final answer:
The United States entered WWII primarily because of the attack on Pearl Harbor, which led to a declaration of war on Japan and subsequent involvement in the global conflict.
Step-by-step explanation:
The United States entered WWII primarily because of the attack on Pearl Harbor. On December 7, 1941, the Japanese launched a surprise attack on the U.S. naval base in Pearl Harbor, Hawaii, causing extensive damage and loss of life. This attack prompted the U.S. to declare war on Japan and enter the global conflict.
While there were other factors at play, such as economic interests in Europe and the sinking of the Lusitania by a German submarine during World War I, it was the attack on Pearl Harbor that directly led to the U.S. involvement in WWII.
The desire for empire expansion, represented by option D, was not a major factor in the United States' entry into WWII.
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