Japan had sworn to "fight to the last man" and it was widely believed that they would virtually do it, as I said projected casualties were expected to be as high as 1 million US and 10 million Japanese, surrender was nowhere in sight.
They asked Japan to surrender, Japan swore to fight to the death.
They dropped a nuke and asked again, Japan swore to fight to the death.
They dropped a nuke and asked again, The Japanese parliament agreed by split decision, and only because the emperor personally recommended surrender.
So by dropping two bombs they saved up to a million American lives.