I researched this for a while some years ago. I'm no professional historian, but I did find some key points that are accurate to the best of my knowledge: The

I researched this for a while some years ago. I'm no professional historian, but I did find some key points that are accurate to the best of my knowledge: The key debate within Japanese leadership was what conditions of surrender to accept. They'd known for some time they were going to lose, but hoped to drag out an invasion of Japan enough to get better concessions, keep the Emperor in power etc. The nuclear bombings ended up not playing a huge role in their decision making. At the time all the major cities in Japan had been firebombed except Kyoto. The fission bomb technology was shocking, but ultimately it meant they did with one bomb what had already been happening via thousands. When the US firebombed Tokyo it killed over 100,000 people in a single night, mostly women, elderly men, and children. McNamara has said he believes he'd have been convicted of war crimes for that had the US not emerged the winner. Russia steamrolling through Manchuria in just under 30 days, utterly routing the Japanese forces there weighed heavily on the minds of Japan's leadership. Once Russia declared war and was clearly committed to being part of the invasion of Japan, they realized they most likely would not be able to extract concessions by further resistance. It's a bit more complex than all that, and there is a debate among historians on details of these points, but I believe it's reasonably accurate. The simple narrative that it saved US lives is a way of avoiding looking at just how ugly things got.