Obviously losing WW2 and the ramifications that ensued saw them lose the empire. However, as with history, it's never wholly as simple as that. Were there any other reasons? Or can it simply be attributed to wholly 'losing the war'
It actually is as simple as that in this case. The terms of Japan's surrender were unconditional and included an acceptance of the Potsdam declaration, which limited Japan's sovereignty to the four home islands.