Final answer:
The Americans sought to avoid helping the Soviet Union with the final defeat of Japan to prevent them from gaining postwar influence in Asia, leading to US-led reconstruction efforts in Japan and the division of Korea.
Step-by-step explanation:
The ally that Americans wanted to avoid helping with the final defeat of Japan due to postwar resettlement concerns was the Soviet Union. As World War II neared its end, the United States recognized that their and the Soviet Union's visions for postwar Europe and Asia were incompatible. While America wanted to promote democratic governments and free-market economies, the Soviet Union aimed to expand Communist influence. Both nations emerged as superpowers postwar, and the US was wary of Soviet expansion into Asia following Japan's surrender. This led to the US taking a dominant role in the reconstruction of Japan to ensure that the Soviet Union did not gain influence over the region, leading to the division of Korea and the establishment of a US presence in Japan.