In the WWII documentary series, Soviet Storm, the creators make claims that the final factor that caused Japan to surrender was not the atomic bombs but the Soviet invasion of Manchuria. The basis of this claim was that Japan had moved the majority of its industry (gasoline, steel, coal, etc) to Manchuria during the war to put it out of reach of american bombers. When the Soviets took control of this land, it decisively removed Japan's capabilities to fight a war.
The episode in question is available here
The narrator details how the will to fight persisted after the atomic bombings and only subsided after losing Manchuria. Coming from a Russian produced documentary, obviously some bias may exist but how accurate are the claims made?
I fully recommend Richard Frank's Downfall for a really thorough look at the various events leading to the end of the war.
The Japanese war strategy by 1945 boiled down to a fairly simple plan: inflict a defeat (or at least a staggeringly bloody setback) on the US forces, then take that opportunity to attempt to negotiate a "surrender" that would leave the Japanese empire intact, with no foreign occupation or loss of territory in the home islands.
The Japanese didn't think the US would be amenable to that formula as proposed, so they wanted to go through a third party, and the third party they had in mind was the Soviet Union. They had a non-aggression pact with the Soviets (which the USSR left in April '45, though by the terms of the pact it should have been in effect another year after that withdrawal), and considered the Soviets the only country that was remotely powerful enough to press the US to accept the offer. More to the point, they considered the threat that Japan might fall into the Soviet sphere of influence to be considerable enough to give the US incentive to negotiate rather than pressing on and driving the Japanese into the Red bloc. (Note they had absolutely no intention of actually doing that!)
The atomic bombs and the Soviet invasion each struck at a different aspect of this plan. With the atomic bombs, the need to invade Japan was reduced, if not completely obviated; the US could literally pound Japan into the stone age without risking large numbers of troops. With the Soviet invasion, the idea of asking the Soviets to mediate went out the window - there's nothing Japan could have offered the Soviets that was better than what a belligerent Soviet Union could simply take.
This was a potent combination. With no plan to bring the US to battle, with no plan to bring the US to the negotiating table, the Supreme Council for the Direction of the War was vulnerable to the Emperor's intervention and the ultimate decision to surrender.
I'm not sure at all that Manchuria at any time contained 'the majority of Japanese industry'
It's like claiming that Germany moved their industry to Soviet Union to put it out of reach of Allied bombers.
One of the major blowbacks for Japan was loss of their possibility to negotiate nicer terms of surrender with US via Soviets.
When Soviet Union entered a war against Japan, chances of that dropped to zero.
The Japanese firmly believed that they could leverage their non-aggression pact with the Soviet Union into an "acceptable" peace treaty. The opinion of the Japanese high command was "it took the Allies 4 years to build this nuclear bomb, it will take them 4 years to build the next one" (the plutonium pit of the 3rd nuke was on a plane flying from the US when Japan finally did surrender). We knew this because we were reading Japan's coded communications. Once the second nuke was dropped, the high command realized that they were not only wrong, but fuckingly fucked.
The Yalta conference required Stalin to enter war against Japan within 90 days of the end of the war with Germany. Depending on how you do the math and count time-zones, Russia declared war against Japan and entered combat on day 89, 90 or 91.
Once the Soviet Union entered the war against Japan, the Japanese high command knew that they had no way to negotiate the surrender that they wanted. The surrender terms they were pushing included returning to Japanese control all islands they held in 1942 (before they started losing territory), prohibition against any "war crimes" trials, that Japanese troops would only "surrender" to Japanese officers (think of this as "returning to barracks") and that the emperor would remain untouchable. The only surrender term that was accepted by the Allies was to leave the emperor on his throne and untouched. It is my personal opinion that this was a mistake - Hirohito should have been hanged as a war criminal.
According to Cook in Japan at War there were 4,335,500 Japanese soldiers in uniform at the time of the surrender with about 3,500,000 stationed outside the "home islands" (mostly stuck in Korea and Manchuria). This was a lot more than the Allies thought that Japan had. Because they were "stuck" outside of the Home Islands, they could not be used to defend Kyushu and Honshu due to naval and aviation blockades.
The Making of the Atomic Bomb and Dark Sun: The Making of the Hydrogen Bomb include lots of details of every nation's atom bomb project. It isn't politically correct to point out that Japan had 2 separate atom bomb projects (a chemical separation facility in Tokyo [which cannot work for reasons of physics] and a gaseous diffusion facility [what the US and all other nations have done] in what we now call North Korea) and that they knew within hours of the Hiroshima bombing what happened.