What if Japan declared war on the Soviet Union after Pearl Harbor?

Hello. I've been thinking about this for a while but couldn't find any threads on that topic. As the title says, what if the Japanese declared war on Britain and the US like they did in OTL but also attacked the USSR at the same time? Will this bennefit either Japan or Germany in any way?
 
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I would think this would overstretch the Japanese supply lines and resources even more. If they're invading China too, it still might be possible for the USSR to collapse, but the Japanese defeat is pretty much inevitable. Earlier collapse?
 
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On the other hand, this slams shut the most productive Lend-Lease route into Russia - no way the Soviets can ship stuff from the US to Vladivostok now.
 
It will throw the Russian war effort into the chaos as they can't move their troops west out of Vladivostok. Moving factories east will be more difficult if you have to worry about a Japanese invasion from that direction. The political effect of Japan invading may result in a political implosion of the Russian government. If someone kills Stalin the government may collapse extending the war by years.
 
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What changed in the Japanese mindset after the Battles of Khalkhin Gol to make them think they could go north AGAIN with success? You will also have to sway the Japanese Navy away from their go-south policies.
 
A more interesting scenario would be if Japan did not go to war with anyone but China and the USSR. If they had limited themselves to these and declared their fight one of anti-communism there's a good chance, they would have secured Manchuria and the Russian east.

But to get back to your question it would depend on how Japan goes to war against the USSR. If they made a deal with White Russian forces in China and established more than a paper thin 'New Russian Empire' they might be able to create a functional puppet state. Just look at all the people that signed on to fight for the Nazis against Russia in OTL.
 
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What changed in the Japanese mindset after the Battles of Khalkhin Gol to make them think they could go north AGAIN with success? You will also have to sway the Japanese Navy away from their go-south policies.
Khalkin Gol was a lot more of a close run thing than most people think. Also, given that the Army was dominant in the government and the Navy was uninvolved in any actions against the Soviets, well...
 
A more interesting scenario would be if Japan did not go to war with anyone but China and the USSR.
While that scenario is an interesting one and would butterfly away many of the problems that eventually screwed Japan later on, I think a big impediment to altering Japanese policy is that Japanese industry had a far bigger need for oil, rubber, etc. (i.e., resources located in the south) than their need for timber, animal pelts, etc. (resources located in the north).
 
This scenario could happen I guess if an accord is reached between the Axis powers in 1940, when they solidified their alliance. Hitler did originally hope that by declaring war on the US, Japan would do the same on the Soviets.

This would create a different strategy than OTL, originally they managed to get the required troops and equipment in Manchuria for a Soviet invasion only by 1942, ~1 mil men and 1k tanks. (24 divisions I think? A purely North strategy would have used up to 60+ so there's that)

They might plan around the idea that the war against the Soviets will end quickly and later being able to move resources to the southern front.

Though I am honestly not sure if this will really create more supply problems than OTL, the Soviet front would mostly depend on Manchurian and Korean infrastructure, while the capacity of fighting in the south would depend on their supply ships, which are not interchangeable.
 
While that scenario is an interesting one and would butterfly away many of the problems that eventually screwed Japan later on, I think a big impediment to altering Japanese policy is that Japanese industry had a far bigger need for oil, rubber, etc. (i.e., resources located in the south) than their need for timber, animal pelts, etc. (resources located in the north).
The resources from the north are still valuable enabling Japan to buy more of the resources it needs. That money can also be used to support independence groups in European colonies for later conquest. Or the Japanese could have conquered the Dutch East Indies while offering all the support the Brits need for their war in Europe and to 'buy' the colonies from the Dutch government in exile. A collapsing Russia means a Germany with far more resources and in a much better position than OTL. Even a Russia limited,broadly, to Siberia and continuing the fight won't be half the threat it was in history.

But we should get back to the authors original question. The additional front may make the Japanese more likely to come to some sort of peace agreement with different enemies.
 
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While that scenario is an interesting one and would butterfly away many of the problems that eventually screwed Japan later on, I think a big impediment to altering Japanese policy is that Japanese industry had a far bigger need for oil, rubber, etc. (i.e., resources located in the south) than their need for timber, animal pelts, etc. (resources located in the north).
There is petroleum up in Eastern Siberia, although to be fair I'm not sure if the technology to discover and extract it was available during the time period this discussion covers.
 
There is petroleum up in Eastern Siberia, although to be fair I'm not sure if the technology to discover and extract it was available during the time period this discussion covers.
Correct. There's a lot of oil in eastern Siberia, however the East Siberian Oil Field is situated well north and west of Lake Baikal. So if Japan was going to push 300-500 miles north and west of Manchuria, then maybe that oils falls into Japanese hands. I viewed a plausible "Japanese Siberian invasion" to be an invasion limited to the Amur region, northern Sakhalin and, possibly, the Kuril/Kamchatka region-- but that's just me reading limiting factors into the OP.

Now there is some oil, and a lot of natural gas under and offshore of Sakhalin Island. But those fields weren't very developed until after 1990 and, besides, Japan was holding the southern half of Sakhalin in 1941. So I suspect that the technology to find and tap into those reserves wasn't available in the 1940's.

The only resources being actively exploited in the Soviet Far East in the 1940's was coal and grain.
 
If Japan wanted to annoy the soviet union, then maybe they should start with Sakhalin!

While it's true that the soviet forces facing Japanese threats had been weakened, is there any reason to believe that Japanese intel knew this? After all, it seemed to be a surprise to the German army to find a whole new army had come from somewhere.
I ask because it's one thing to open a new front with clear and achievable objectives when you know your enemy is both busy and weakened, but if you think they are just as strong as last time (when you lost) or maybe even stronger that's not going to look like such a good idea.
The OTL decision to allow enemy ( USA) ships to travel unmolested to and from the USSR suggests that they either thought it wasn't safe to attack the USSR or that they thought it wasn't worth it. If the former, they might have a go if not fighting the USA, but if the latter then it's still not worth it unless they can walk in unopposed.
 
Its baffling in hindsight that the Japanese didnt think SU should be prioritized. Japan can never win on its own and only Germany winning offers the Japanese any prospects of success.
In such a scenario getting Spain in on the Axis side would be critical. KM and air power based their would shut the southern route and ensure Japan a free hand against the British (eg, the Germans could have offered something back). Indeed, a close Accord between the axis in 1940 is a major missed opportunity.
 

thaddeus

Donor
A more interesting scenario would be if Japan did not go to war with anyone but China and the USSR. If they had limited themselves to these and declared their fight one of anti-communism there's a good chance, they would have secured Manchuria and the Russian east.

another scenario would be to go to war with the UK once the Axis pact had been signed, move on Hong Kong, British Borneo, and then Singapore. they could join the war against the USSR on some conditions, say once Leningrad had been captured and the Pacific Lend-Lease route becomes that much more important?
 
I'm afraid this is turning into a spaghettified mess on my part-
I would think this would overstretch the Japanese supply lines and resources even more. Probably would see a Japan collapse ≈ early 1945, actually.
The first part makes sense, as Japanese shipping was pretty limited, though some of that may be mitigated by using coastal vessels that couldn't have supplied say, Tarawa. The second part though, I'm not sure what you're basing it on. It isn't like nukes, American oilers and the like are going to be rolling out any faster.
On the other hand, this slams shut the most productive Lend-Lease route into Russia - no way the Soviets can ship stuff from the US to Vladivostok now.
Vladivostok is screwed. I suspect that it'll eventually flow through the Euro/arctic route, but that's got loads of issues.
Khalkin Gol was a lot more of a close run thing than most people think. Also, given that the Army was dominant in the government and the Navy was uninvolved in any actions against the Soviets, well...
I'm going to disagree, in part. Kalkin Gol/Nomohan saw the IJ troops do OK in the field, generally inflicting more losses, for instance, but the Soviets were able and willing to ship so much more force to the area that even had the Japanese had successes, they'd have been defeated in the "2nd" Nomohan. This troop moving ability was central to Soviet strategy and planning, and central to all their successes. Look at Bagration. Bret Deveraux calls that the "operational" level of warfare, and it was the one piece the Soviets excelled at.
I once read on this forum that the soviets would allow the US to start basing long range bombers out of Russia
I'm skeptical. Getting them there and supplying them would be a nightmare, and the Japanese are probably going to be advancing through those areas. I bet it'd be done somewhat, but but just like historically, the main bomber blows will probably come through Saipan and the like.
Its baffling in hindsight that the Japanese didnt think SU should be prioritized. Japan can never win on its own and only Germany winning offers the Japanese any prospects of success.
Imperial Japan is baffling, period. Struggling in a war against China, and starting wars against the US and UK as side quests to that just doesn't fly.
That said, and as I noted, The absurd ability for massing troops and equipment that the USSR showed at Kalkin Gol was probably a big turn off for a war against them.
 
While it's true that the soviet forces facing Japanese threats had been weakened, is there any reason to believe that Japanese intel knew this? After all, it seemed to be a surprise to the German army to find a whole new army had come from somewhere.
In 1940, the Japanese estimated that the Soviet forces stationed from Vladivostok to Mongolia consisted of thirty rifle divisions, two cavalry divisions, nine tank brigades and one mechanised brigade.

Their estimate was somewhat off, especially where it came to the extent of mechanisation - the Red Army in Asia actually boasted nineteen rifle divisions, six tank divisions, four mechanised divisions, two motorized rifle divisions, one cavalry division, and ten rifle brigades.

A proportion of these forces were hurriedly moved westward when Barbarossa hit (these were the reinforcements that surprised the Germans with their appearance as you say); the best chance the Japanese would have in a 'strike north' move would therefore be to coordinate the timing of their offensive with that of the Germans.
 
There was for decades a lack of accurate information on what the Soviet Union had in Soberia, in the Far East, and the Eastern maritime provinces in military power, This has grown into a persistent myth the Far East was stripped of armies to save Moscow or the western USSR
In 1940, the Japanese estimated that the Soviet forces stationed from Vladivostok to Mongolia consisted of thirty rifle divisions, two cavalry divisions, nine tank brigades and one mechanised brigade.

Their estimate was somewhat off, especially where it came to the extent of mechanisation - the Red Army in Asia actually boasted nineteen rifle divisions, six tank divisions, four mechanised divisions, two motorized rifle divisions, one cavalry division, and ten rifle brigades.

A proportion of these forces were hurriedly moved westward when Barbarossa hit (these were the reinforcements that surprised the Germans with their appearance as you say); the best chance the Japanese would have in a 'strike north' move would therefore be to coordinate the timing of their offensive with that of the Germans.

From the 1970s and more particularly post 1990 research has show the Soviet Far Eastern Armies and Maritimes forces were stronger than supposed. and the fresh forces that 'saved Moscow' were largely from populated regions of Siberian much further west, nearer the Urals and the trans Ural regions. This web site has a daily clear summary of what the Red Army strength was in the Far East, what the trained reserves were, and what of the mobilized forces was actually sen west.

 
On the other hand, this slams shut the most productive Lend-Lease route into Russia - no way the Soviets can ship stuff from the US to Vladivostok now.

This is correct for the overall war 1941-1945. But... When the Soviet leaders understood the breakdown of US/Japanese negotiations, and understood Japans government had made a decision for war they took precautions. The agency controlling Soviet maritime cargo shipping began in the early Autumn of 1941 redirecting its Pacific cargo fleet elsewhere. By November the bulk of the cargo fleet was headed to safer waters & only a few ships containing critical cargos risked the trans Pacific voyage. Once it was clear the Japanese were not going to attack the USSR the trans Pacific route was revived, but the traffic was increased only slowly. This was in part because the USSR rebuilt its Pacific cargo fleet with new construction, mostly Liberty class ships from the US. Bottom line is 1942 saw relatively little material delivered vis the Pacific & trans Siberian railways. There is a web site or two that shows the quarterly or monthly trans Pacific deliveries 1941-1945.

Beyond that the quantity of material delivered under the First and Second Protocols of the US/USSR Leand Lease agreements, that covered 1941-mid 1943 was not the bulk of 1943-45. Critical items, but not the gross tonnage after mid 1943.
 
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