The Japanese feared a Russian invasion. We could have negotiated a surrender using these fears. Japan’s army was beaten and could not sustain the fight against American and Russian forces.I agree it was barbaric.
On the flip side, civilians were intentionally being killed by both the Axis powers and the allies since 1940. Sometimes, in huge numbers
It is open to debate if the Japanese were ready to surrender.
But surrender was only part of what we needed to accomplish.
We needed Japan to submit to outright military occupation, and the forcible dismantling of their government, prosecution of their leadership for war crimes, and to have a democratic government with a pacifist constitution forced on them.
That type of occupation and coercion was really the only solution to put an end to the Japanese warrior ethos and a militaristic nation which had spent decades attacking and occupying its neighbors.
Whatever his faults were, Truman recognized this vision as the ultimate solution to a militaristic and belligerent Japan. And 70 years of history since 1945 has proven this vision to be prescient.
The use of nuclear weapons were not necessary.