> Starve them out. The allies had submarines all around Japan and completely blocked all food and oil imports. This was working. But given the Japanese fighting spirit, likely tens of millions would have died before any change took place. It's also possible that the population could drop so low that the islands would become self-sufficient and then the war would drag on literally forever.

Probably the biggest share of the blockade at the end was done by naval mines. At the end, the US airdropped naval mines in Japanese harbors to prevent them from importing food, and this sunk more Japanese shipping than the submarines ever did. It was even called “Operation Starvation”.