[LeoXiao]

Originally Posted by DonQuigleone

Yes, but what of the German factor? Soviet/Japanese engagements don't take place in a vacuum. The Japanese engaging the Soviets in Siberia would have severely reduced their strength in the west. One of the reasons the Soviets was able to stop the German advance was due to the transferral of the more experienced troops from the Far East, which was only possible because they were sure (due to Espionage) that the Japanese were not going to attack.

The issue is that the far east Siberian divisions were never sent west, and only had minor percentages of their forces taken to the west as reinforcements. The "Siberian" troops that did partake in fighting against the Germans were from Central Asia.
What would not have been possible in 1942 is for the Russians to fight the Japanese and conquer all of Manchuria, but they would've beaten the Guandong army on the border regions just as easily as in 1939, due to reasons listed above.

If the Japanese had chosen not to attack America at Pearl Harbour, and instead concentrate on defeating the soviets as the Germans attacked from the west, who knows how things could have been different?

The beginning of the Pacific War against the USA and European colonies was a massive strategic mistake, but did not fundamentally detract from the IJA's abilities in waging land war. Either way, the Japanese land forces were still bogged down in China and they were still inferior to their Soviet counterparts. So the only chance they have in beating Russia is to have not gotten involved in the invasion of China in 1937.

Either way, there was clearly an error of communication between Germany and Japan. They were quite uncoordinated considering they shared common enemies. If they could have defeated the Soviets, defeating the rest of the Allies would have been significantly easier.

I agree that the Germans and Japanese did not coordinate well. Partly this is because they were only allied in 1940, by which point the Japanese were already set on going south and east, not north.

Had Hitler allied with Japan in the mid-30s, before China proper was invaded, it would've provided more incentive to prepare to attack Russia in tandem with Germany. However I doubt that the Japanese at that point realized exactly how badly they needed whatever help they could get.

Originally Posted by Ithekro

The Armies plan has been to take Siberia for resources. The Soviets proved too difficult so the plan was scrapped and the Navy was listened to for once.

The Japanese saw China as their main target in the grand scheme. They jumped into the Chinese front too fast and too deeply, attacking Siberia with only a half-hearted effort. The Chinese war also led to their bankruptcy and the embargo by the US.
The Japanese also needed resources, but I don't know where those Siberian deposits lay. Siberia is big and the more remote the resources are the less the Japanese will be able to conquer or exploit them.