Japan's surrender - was it the a-bombs or Soviets?

The correct answer IMHO is ‘both’, but how much of an impact did they make respective to each other? A spin off of this thread about whether you’d drop the bombs, the impact of the USSR’s declaration of war came up. How much of an impact on Japan’s surrender do you think the dropping of the bombs was, weighed up with the impact of the Soviet declaration of war?

Poll incoming, ‘100 - bombs’ is if you think the bombs did it all, ‘100 - Soviets’ is if you think it was all the USSR and the bombs did nothing. Weighed up just against each other, not counting in any other factors; meaning if we count the combined impact of both on the surrender as the ‘100’, how much of a role do you think the specific factors played in ending the Second World War. Hope that makes sense.

Just spit-balling I’d probably put it at about a 40/60 split between the bombs/Soviets, though I could be tempted possibly as far as 30/70. Whadya reckon?

I said this in the other thread. Even though Japan was on their side of the world they couldn’t be bothered until 3 days AFTER the first nuclear weapon was used. They posed no threat to a country under nuclear attack.

Based on a reading of the Japanese Wikipedia, the bombs appear to have been a secondary consideration. Nearly all of the details given are about their expecting to be able to negotiate a non-compete with the USSR and then, suddenly, being surprised when the Russians decided to declare war.

And I do know that one of the central concepts behind attacking China, to start the war, was to prevent the spread of Communism from hitting Japan. So it would seem a bit plausible that the fear of being overtaken by the Commies would be a bigger concern (for the elite) than the risk of losing more peasants.

(I accidentally selected 80/20 instead of 20/80.)

I don’t think they saw the Soviets as doing much more than they did; grabbing some land at the end. To the homeland and home population it was more the US/UK threat and the bomb of course after that card was played.

I’ve exhausted myself with my arguments in the other thread. I 'll go with 60% bombs.

It’s important to remember that the Soviet role wasn’t just invading Manchuria; it was also the closing off of the one strong diplomatic channel the Japanese thought they had for negotiating better peace terms.

You left off the most important option: “It was both, but impossible to say which was more because the events occurred concurrently and we can’t tell for certain.” I voted 50/50 since that was the closest option.

I’ll try to post more, but for anyone who voted the Soviets at less than 40%, you really need to study this more thoroughly. Likewise, I would like to see an in depth argument, because neither of those positions can be supported by what we know.

I always figured it was kind of 6 of one, a half-dozen of the other, and the combination of both is what broke the Japanese. Had they been in reverse order, the result would probably have been the same.

Look at it this way… you’re sitting there, with your country being mercilessly bombed every night, your navy mostly on the bottom of the Pacific, and an angry United States massing troops, ships and airplanes in a grimly resolute effort to END the war, whatever that takes. Definitely not an optimistic situation.

Then you hear that they obliterated one of your cities outright in a single explosion and hear Truman’s “rain of ruin” speech. Terrifying, but you don’t know if it’s a bluff, or if they really do have more bombs like that. Then you hear 3 days later that the Russians have invaded Manchuria and declared war. And the same day, you hear that the Americans have obliterated another city instantly.

Why would it have been any different had it been Soviet invasion/declaration of war on Aug 6 with Hiroshima, and Nagasaki on Aug 9?

There’s no good way to know for sure, although I doubt that the Japanese were disregarding the atomic bombing as much as that historian seems to imply. My suspicion is that the Nagasaki bombing convinced them that Hiroshima wasn’t a one-off or flukey thing, and that Truman’s “rain of ruin from the air” was a real and imminent thing, and that between it and the Russian invasion of Manchuria/Declaration of War, it was time to surrender.

I’m sticking with 100% bombs.

The Russians promised to declare war on Japan in 1943, after Germany was defeated. The Japanese knew this. Russia’s declaration was not news to Japan in any way shape or form. The very fact that the Russians were prepared to invade on the exact day of their promised deadline means the Japanese must have had intelligence on things like Russian troop movements making that invasion possible. They knew all of this well before the surrender.

What was new? A giant super bomb that allowed a single plane to level a whole city. That’s what mattered.

This is completely false. Japan was trying to get the Soviets to help negotiate a favorable peace treaty all spring and summer. While the Soviets gave notice to Japan that the neutrality treaty was canceled, it had a 12 month period until the cancellation became effective, something the Soviets stressed.

Japan knew that the Soviets were moving some troops East. It was basically accepted given that they had moved so many West for the European war. But Japanese intelligence wasn’t predicting an imminent attack.

The Japanese were caught completely by surprise by the Soviet declaration of war and the invasion.

Regardless of whether they expected anything or not, the rapid collapse of the Japanese Army in Manchuria was an even bigger surprise. This was the final nail in the coffin of the Emperor’s trust in the military. That the military knew that everything was was gone, both militarily and politically, meant the Emperor could finally move forward.