It is called History my friend. Yes America was winning the war in the Pacific but it still needed troops to ensure that win. Also America used its "nukes" (actually it was an Atomic Bomb that was dropped on Hiroshima and a Plutonium Implosion Bomb that was dropped on Nagasaki) for 2 reasons: 1. To avoid a land invasion of Japan after they failed to agree to the US terms of surrender. The US wanted to strip Japan of ever having another Emperor but they refused, the Bombs were dropped and the Emperor actually stepped in and made the government surrender. 2. As a show of power to Russia, to stop them getting any ideas during the clean up after the war. Russia had already turned on 2 of its initial allies, German and Japan and the US didn't want them doing it a 3rd time.