The correct answer is:
The United States entered World War II, making the Allies stronger and better equipped to defeat the Axis powers.
When Japan attacked Pearl Harbor on December 7, 1941, it prompted the United States to enter World War II. This event marked a significant turning point in the war. The United States joining the Allies brought in additional resources, manpower, and industrial capacity, significantly strengthening the Allied forces. The entry of the United States into the war played a crucial role in eventually defeating the Axis powers.