Suppose the Allies decide not to drop the Bomb on Hiroshima or Nagasaki. In fact let's say they decide to not drop the bomb on Japan, at all.
Was there any alternative way to defeat Japan? That is apart from an invasion?
The Americans had a tight blockade around the Japanese home islands and they were basically bombing the Japanese cities to rubble. Could they have just held off on an invasion indefinitely? Could they have just choked the Japanese economy into collapse and thus gotten the Japanese to surrender?
USN RAdm (then Captain) Dan Gallery (he that captured the
U-505) was then an alternate member of the Logistics Committee of the Joint Chiefs of Staff. The plans for invasion of Japan came before the Logistics Committee on a day when Gallery was sitting. He suggested that it was not necessary to invade Japan, because Japan would collapse from the Allied blockade. The response was...
discouraging. In Gallery's own words: "I should have stood in bed. The Army and Air Force members looked at me as though I had puked on the table."
Could such a surrender have led to a Japanese version of the 'stabbed in the back' myth?
Probably not, because by the time Japan surrendered, pretty much all of Japan's overseas empire would be lost.
Perhaps Japanese warrior culture where defeat is unacceptable might stop them from giving up so soon. But would they not give up eventually?
Well, here's a point. The last fantasy plan of the military hardliners was that when the US forces landed in the Home Islands, the Japanese would hit them with gigantic banzai attacks using the entire population, i.e. women and children with pointy sticks. This would inflict such heavy casualties on the US that it would shock the "soft" Americans, who would agree to a negotiated peace on Japanese terms.
If the US ostentatiously doesn't invade, this fantasy collapses.
How much more would it cost in allied lives to continue the typical bombing and blockading compared to an invasion?
Much fewer, in terms of direct military casualties.
How many more civilian deaths would occur from such a bombing and blockading campaign?
Japanese civilian deaths? More than immediate surrender, I guess. Because the bombing and blockade would continue unabated, invasion or not.
Though most of these deaths would not be from Allied military action, but from starvation and epidemic disease, as Japanese food production and public health broke down.
Note, thought, that there would also be millions of deaths outside Japan, due to starvation, disorder, and murder by Japanese occupation forces. The hardliners planned to order the murder of all Allied PoWs and civilian internees, to begin with. And the death toll from Japanese misrule in China was enormous.
Nonetheless, it's difficult to imagine the hardliners ever admitting that surrender is compelled, and without the terrifying shock of atomic bombs, the "rational" faction might never get Hirohito to intervene.
There is one scenario I've thought of that might work. Suppose, after the occupation of the Philippines, US forces landed on the Chinese coast and pushed inland to link up with Chinese forces. Then the US and China begin a massive operation to equip and train lots of Chinese troops. The Allies clear the Japanese from south China, and then from Shanghai-Nanking and toward Peking, with Chinese troops doing most of the grunt work. There are public references to Chinese troops joining the invasion of Japan, with Chiang and other Chinese leaders talking about marching through Tokyo. Now that last fantasy of the hardliners is worthless - because the Chinese will not back off due to any amount of casualties the Japanese can inflict. The campaign in China shows that the Chinese (with some US help) will win. And Chinese conquest of Japan will be... ugly. Better to quit now.
A potential US-Soviet invasion of Japan has much of the same potential, especially after a Soviet blitz of Manchuria and Korea.
