The popular narrative surrounding and rationalization of the dropping of the atomic bombs by the US on Japan is that it ultimately saved lives by causing the Japanese surrender and eliminating the need for an amphibious invasion.
However after reading on the subject, it seems by far the primary reason Japan capitulated was because of the completely unforeseen declaration of war and subsequent invasion by the Soviet Union, which almost overnight annihilated their vaunted Kwangtung Army and seized their Manchurian territories. And in fact, the atomic bombs made little impression on the Japanese, whose cities were already being virtually obliterated by the the conventional US strategic bombing campaign. Thus the atomic bombs really made little to no difference on the Japanese surrender, killing hundreds of thousands of civilians potentially needlessly.
Is there any merit to this perspective on the Japanese capitulation?
It is very likely that Japan would have surrendered without the atomic bombing. Eventually.
However, the combination of the Soviet entry into the war and two atomic bombs only just tipped the government towards surrender (and even then there was a coup attempt in order to avoid surrender), and it is likely that it would have taken longer before Japan surrendered without the atomic bombs.
Can we estimate deaths due to a delay in surrender? In 98 months of war in China, Japan killed about 4,000,000 civilians and POWs (counting massacres, executions, civilian deaths in battle and bombing, and deaths of forced labourers, but not counting deaths due to famine or disease), an average of 40,000 per month. In 45 months of WWII, Japan killed about 2,000,000 civilians in occupied and colonial Asia, an average of about 45,000 per month (counting massacres, executions, civilian deaths in battle and bombing, and deaths of forced labourers, but not counting deaths due to famine or disease). Adding military deaths in China (about 2,000,000) and famine deaths (about 10,000,000) quadruples the death rate in China, to about 160,000 per month. Adding famine deaths to WWII approximately doubles the death rate in occupied Asia, to about 90,000 per month. Thus, the war in China and the occupation of much of SE Asia was killing people at about 250,000 per month. This is an average over the war, and the death rate was higher late in the war.
The surrender also stopped the fighting in Manchuria, saving many Japanese lives (and also many Soviet lives and civilian lives). The Japanese forces in Manchuria fought hard, but generally did not fight to the death. Estimating Japanese military deaths as the geometric mean of the Japanese and Soviet claims, about half of the Japanese troops who fought the Soviets died, and about half surrendered. Approximately 600,000 Japanese troops were interned by the Soviets after the surrender; we can estimate that if they had fought, there might have been another 300,000 Japanese military deaths. There would have been many Soviet and civilian deaths, too.
If Japan had surrendered about a month later, the above considerations give an estimate of about 250,000 civilians deaths in China and occupied Asia, and about 300,000 additional Japanese military deaths, without including further civilian deaths in Manchuria or deaths in Japan from US (non-atomic) bombing. it seems quite reasonable to claim that the atomic bombings accelerated the Japanese surrender, and in doing so saved lives.
It's worth pointing out that the Soviet invasion wasn't completely unforeseen, the Kwantung army was no longer vaunted, and it wasn't annihilated overnight.
Molotov had told Ambassador Sato on April 5th that the Soviets intended to end the Neutrality Pact. The Japanese still hoped to either convince the Soviets to aid them in the fight against the US, provide resources, or at least negotiate an end to the war that did not require Japan to unconditionally surrender. But they were very well aware of the massive redeployment of troops to the Manchurian border. Military leadership had issued a standing order several months prior to the invasion to conduct a fighting retreat into Korea in the event of a Soviet invasion. The timing was a surprise, but not the fact that the Soviets invaded.
By 1945, the war in Manchuria had long been over, and most of the best divisions had been transferred to China or elsewhere in the Pacific. In the previous few months, 5 divisions had been transferred from Manchuria to Kyushu in preparation for the Americans. When Suzuki asked Lt Gen. Sumihisa Ikeda, who had recently transferred from Manchuria if the Kwantung army could repulse the Soviets, he replied, "The Kwantung Army is hopeless."
As far as the actual invasion, the western thrust was mostly bogged down in the Gobi desert and the Great Kinghan Range suffering from a lack of fuel and meeting no resistance. Meretskov's First Far Eastern Front met heavy resistance in Mutanchiang and Chongjin. The majority of the fighting occurred in those two cities from August 9th until the 15th when the Japanese surrender ended the war.
Racing the Enemy - Tsuyoshi Hasegawa
140 Days to Hiroshima - David Dean Barrett
/u/restricteddata has previously answered Did the atomic bombings in Japan indirectly prevent the deaths of more Japanese citizens than they killed? and Did the US have to nuke Japan in WWII?
/u/t-o-k-u-m-e-i has previously answered Was it the bomb, or the Soviet declaration of war that ended WWII? (in the Pacific)
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