The war against Japan was decided by the respective navies and the naval war against Japan was almost entirely an American enterprise. The navies determined where the armies could go and how they were supplied. With the Imperial Navy defeated, Japan was defeated.
Yes, however, don’t forget that the Brits and the Indians kept the Japanese off the eastern borders of India and the Chinese also kept Japan quite tied down. the US was the main (>80%) of the win against Japan, but it wasn’t a single-handed win.