Even though the Atomic bombs were dropped after the defeat of Japan was an obvious eventuality, the assumption that they were on the verge of surrendering is not really all that well supported; and with the tactics used by the Japanese (kamikaze bombers) it would have been reasonable to assume that the Japanese citizens and their leaders would see throwing their lives away in a futile effort to avoid defeat as honorable. Realistically, the death count to Japanese citizens would have probably been an order of magnitude worse if the United States and their allies were forced to take Japan using conventional tactics; and it is plausible that without the Nuclear strike the citizens of Japan would have resisted the United States and their allies even after Japan was captured, resulting in an insurgency which could have had a recurring death toll for decades.
Basically, the Nuclear strikes demoralized the Japanese to such an extent that the war was over instantaneously; and even those that were against the occupation of Japan feared the consequences of resisting the Americans. Millions of lives (potentially tens of millions of lives) were saved and the country was instantaneously stabalized because of these weapons. Could you imagine how many people would have died if the Americans would have needed to invade Japan? Could you imagine how long the Japanese could have maintained an insurgency had it been backed by the USSR in an attempt to create a communist nation?
