Why was Japan so successful in expanding its territory in 1942?

Japan expanded rapidly in 1942 partly because most U.S. military forces were not in the Pacific theater, so Japan did not face the majority of U.S. forces at once. The attack on Pearl Harbor also weakened the U.S. Pacific Fleet temporarily, giving Japan an opportunity to seize territory. Thus, the best answer is “It did not have to fight the majority of US forces.”

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