Why did Japan surrender to the US?

Possibly both, in a way. By the end of the war the Japanese military wanted to continue the war. They believed in the glory of a beautiful death. But the war ended because of a decision of the Emperor. No one knows exactly what made the Emperor decide to surrender. It could have been because of the Atomic Bomb, but the damage and death done to Tokyo by fire bombings was greater than the damage and deaths resulting from the A-Bomb. Sill the power of a single bomb from a single plane must have had some influence. On the other hand the Japanese feared the Russians, having fought them several times in the past. It was obvious that the longer the war lasted the more likely the Russians were to take over the northern island of Hokaido, perhaps even more. They might have even taken parts of the main Japanese island of Honshu. The ONLY way to prevent that was to end the war before the Russians could invade. It is most likely both factors influenced the decision of the Emperor, but we will never know for sure. Hope this is of some help, John *It was probably both of them, because they both tried their best to win over Japan. It was mostly because America bombed Japan.