Answer:
Japan signed a neutrality treaty with the Soviet Union on April 13, 1941, to avoid a two-front war with the Soviet Union and the United States. Japan was already at war with China and was planning to expand its empire in Southeast Asia. However, Japan was concerned about the possibility of the Soviet Union attacking from the north, which would have stretched Japan's military resources too thin. Therefore, Japan signed the neutrality treaty with the Soviet Union to ensure that it would not have to fight a war on two fronts. This allowed Japan to focus its military efforts on its expansion in Southeast Asia. However, the neutrality treaty was short-lived, as the Soviet Union declared war on Japan in August 1945, just before Japan surrendered to the United States.