I disagree with this. The US had effectively cut Japan off from the resources they needed to fuel their war efforts. All that we had to do was sit back and starve Japan of oil and precious minerals until they were willing to surrender. The allies didn't really need to invade. The problem was that the US were not content to just let Japan starve to death behind the US naval blockade of the island nation. Otherwise an invasion would have come at great loss to US lives than the firebombing campaigns. Oh and don't forget all those people who died from incinerary bombs. Did you happen to know that the US firebombing explicitly avoided these cities, knowing that they would be the A-bomb targets? It's not like they could have driven the populace to evacuate with a few conventional attacks before that.