Japan by 1941 was in no shape to fight the Soviet Union on land. This was due to the undeclared border war at Khalkin Gol between the two powers in 1939 in which the Soviet Union bloodied the IJA. This made the Japanese government and high command to switch strategies, instead of expanding north, they would continue their expansion southward into its already hold on China and possibly European colonies. Japan’s army was a good military force, however it was prepared to fight colonial or garrison troops and Asian armies. Which were ill equipped and not as well trained as the average Japanese soldier. While the Navy would destroy any reinforcements and other fleets that tried to counterattack.

By 1941, Japan signed the Soviet-Japanese neutrality pact which would make both sides abstain from attacking each other. When Barbarossa began Japan noticed Russia started to buckle under the pressure of the German advance, but not collapsed. Japan knew after Khalkin Go that it stood no chance against Russia in a land war. Japan was ill equipped and too spread out to really focus on Russia. Japan was now fully committed into attacking the US and other European powers in Asia after the US embargoed Japan. This cut off metals like iron and copper and more importantly oil to Japan, who relied heavily on imports. This really forced Japan’s hand because without those resources, it could not carry out its operations on land or sea. While Europe was in turmoil because of Germany, Japan planned to take the British and Dutch colonies which had many resources it needed. But first it had to take out the US and it’s fleet.

Japan was also spread thin due to the war in China. These troops would have to be sent to Manchukuo to give the Japanese Army a fighting chance against the Russians. And after years of war and destruction they caused in China, would the Chinese just let them go if they offered a peace treaty? No they would keep fighting and possibly disrupt their planned attack on Russia.

Even if Japan could have attacked Russia, it wanted it to be in complete turmoil or a cakewalk. They couldn’t risk Russia being just off balanced and could come back someday and counter attack. Japan can’t risk a massive ground operation when it’s already launching a massive naval operation against the US, UK, and Dutch. While Germany and Japan were “friends” they weren’t a unified high command or willing to cooperate as much as the Allies did. Japan was in no position to fight the Soviet Union and it’s resource problem would only get worse if they invaded the Soviet Union. It’s decision to instead turn South was the better option as it could rely on its more powerful Navy, and could secure resources much quicker than in Siberia.

Hey there,

Just to let you know, your question is fine, and we're letting it stand. However, you should be aware that questions framed as 'Why didn't X do Y' relatively often don't get an answer that meets our standards (in our experience as moderators). There are a few reasons for this. Firstly, it often can be difficult to prove the counterfactual: historians know much more about what happened than what might have happened. Secondly, 'why didn't X do Y' questions are sometimes phrased in an ahistorical way. It's worth remembering that people in the past couldn't see into the future, and they generally didn't have all the information we now have about their situations; things that look obvious now didn't necessarily look that way at the time.

If you end up not getting a response after a day or two, consider asking a new question focusing instead on why what happened did happen (rather than why what didn't happen didn't happen) - this kind of question is more likely to get a response in our experience. Hope this helps!