Why didn't Japan invade the Soviet Union during WW2?

It astonishes me that this is not better understood as it is actually central to the  whole development of  WWII.  I have been barely conscious of this part of the war and i have read extensively on all this.  Obviously i am not alone in this oversight.

This war gave the Russians a battle hardened army in the East while everything opposing Germany was anything but.  In fact that army of millions would have been drained of talent to fight against Japan.

It also tells why Stalin wanted peace with Germany to last a while.  As it turned out, Pearl Harbor effectively released that Eastern Army to rush west to Moscow and throw back the German Army there.  And yes they knew that Japan was not going to attack them a lot sooner.  Pearl Harbor merely locked the door.

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Why didn't Japan invade the Soviet Union during WW2?

Interesting, Japan was brave enough to attack US. Soviet Union was the closest country of all natural resources to feed Japanese navy.

Sohail Khurianwala,

 https://www.quora.com/Why-didnt-Japan-invade-the-Soviet-Union-during-WW2/answer/Sohail-Khurianwala

Many people who study about World War II are not aware of this:

The forgotten Soviet-Japanese War of 1939

Japanese battle plan

From May to September 1939, the USSR and Japan fought an undeclared war involving over 100,000 troops.

This war played its part in altering world history.

In the summer of 1939, Soviet and Japanese armies clashed on the Manchurian-Mongolian frontier in a little-known conflict with far-reaching consequences.

This was no mere border clash, this undeclared war raged from May to September 1939 embroiling over 100,000 troops and 1,000 tanks and aircraft.

Some 30,000-50,000 men were killed and wounded. In the climactic battle, which lasted from August 20-31, 1939, the Japanese armies were encircled and crushed by Soviet Armor in the Far East.

This coincided precisely with the conclusion of the German-Soviet Nonaggression Pact (August 23, 1939) – Which gave Hitler the green light he wanted to invade Poland and the outbreak of World War II one week later when only Britain and France declared war on Nazi Germany.

These events are all connected.

This not so famous conflict also influenced key decisions in Tokyo and Moscow in 1941 that shaped the conduct and ultimately the outcome of World War II.

This conflict (called the Nomonhan Incident by Japanese, the Battle of Khalkhin Gol by Russians) was provoked by a notorious Japanese officer named Tsuji Masanobu, ring-leader of a clique in Japan’s Kwantung Army, which occupied Manchuria in the 1930s.

On the other side, Georgy Zhukov, who would later lead the Red Army to victory over Nazi Germany, commanded the Soviet forces.

In the first large clash in May 1939, a Japanese punitive attack failed and Soviet/Mongolian forces wiped out a 200-man Japanese unit. Infuriated, Kwantung Army escalated the fighting through June and July, launching a large bombing attack deep inside Mongolian territory and attacking across the border in division strength.

As successive Japanese assaults were repulsed by the Red Army, the Japanese continually upped the ante, believing they could force Moscow to back down. Stalin, however, outmaneuvered the Japanese and stunned them with a simultaneous military and diplomatic counter strike.

In August, as Stalin secretly angled for an alliance with Hitler, Zhukov amassed powerful forces near the front. When German Foreign Minister Joachim von Ribbentrop flew to Moscow to sign the Nazi-Soviet Pact, Stalin unleashed Zhukov’s forces on the Japanese.

The future Red Army Marshal unveiled the tactics he would later employ with such devastating effect at Moscow, Stalingrad, Kursk, and elsewhere: a combined arms assault with massed infantry and artillery that fixed the enemy on the central front while powerful armored formations enveloped the enemy’s flanks, encircled, and ultimately crushed him in a battle of annihilation.

Over 75 percent of Japan’s ground forces at the front were killed in combat. At the same time, Stalin concluded the pact with Hitler, Japan’s nominal ally, leaving Tokyo diplomatically isolated and militarily humiliated.

The fact that the fighting at Nomonhan coincided with the German-Soviet Non-Aggression Pact was no coincidence.

While Stalin was openly negotiating with Britain and France for a purported anti-fascist alliance, and secretly negotiating with Hitler for their eventual alliance, which divided territory in Eastern Europe between the USSR and Nazi Germany, he was being attacked by German’s ally and anti-Comintern partner, Japan.

By the summer of 1939, it was clear that Europe was sliding toward war. Hitler was determined to move east, against Poland. Stalin’s nightmare, to be avoided at all costs, was a two-front war against Germany and Japan. His ideal outcome would be for the fascist/militarist capitalists (Germany, Italy, and Japan) to fight the bourgeois/democratic capitalists (Britain, France, and perhaps the United States), leaving the Soviet Union on the sidelines, the arbiter of Europe after the capitalists had exhausted themselves.

The Nazi-Soviet Pact was Stalin’s attempt to achieve his optimal outcome. Not only did it pit Germany against Britain and France and leave the Soviet Union out of the fight – it gave Stalin the freedom to deal decisively with an isolated Japan, which he did at Nomonhan. This is not merely a hypothesis. The linkage between Nomonhan and the Nazi-Soviet Pact is clear even in the German diplomatic documents published in Washington and London in 1948.

Recently revealed Soviet-era documents add confirming details.

Soviet General Zhukov won his golden spurs at Nomonhan/Khalkhin Gol – and thereby won Stalin’s confidence to entrust him with the high command, just in time to avert disaster in December 1941 when the spearheads of the Wehrmacht were just 20 miles from the spires of the Kremlin.

Zhukov was crucially able to halt the German onslaught and turn the tide at the gates of Moscow in early December 1941 (arguably the most decisive week of the Second World War) in part by deploying most of the forces from the Soviet Far East.

Many of these were the battle-tested troops he used to crush the Japanese at Nomonhan. The Soviet Far Eastern reserves – 15 infantry divisions, 3 cavalry divisions, 1,700 tanks, and 1.500 aircraft – were deployed westward in the autumn of 1941 after Stalin learned from his master spy - stationed in Tokyo - Richard Sorge (pronounced - Rishart Zorga) that Japan would not attack the Soviet Far East, because it had made an irrevocable decision for a southward expansion that would lead to war with the United States and Britain.

Japan decided to gamble on using its powerful Navy to wallop the Americans and British since it did not forget the whacking its Army had received from the Soviets on the Soviet Manchurian border in 1939.

There were other considerations also.

It was the oil embargo imposed by the USA and Britain on the Empire of Japan after it overran French Indo-China, after the fall of France in 1940 to the Wehrmacht, which forced Japan to look desperately for oil and other resources vital for the survival of her empire in the East.

By September 1941, with the oil embargo by the USA and Britain in force, Japanese oil reserves had dropped to 50 million barrels, and their navy alone was burning 2,900 barrels of oil every hour.

The Japanese had reached a breaking point. If they did nothing, they would be out of oil and options in less than 2 years, If they chose war, there was a good chance they could lose a protracted conflict.

Given the possibility of success with the second option, versus none with the first option, the Japanese chose war.

Importantly, Siberian petroleum zones are the West Siberian petroleum basin, Central Urals, Sakhalin Island.

Eastern Siberia did not have the extensive oil wells like those which were established in the Dutch East Indies at that time.

The Japanese leadership thought that securing the oil wells of the Dutch East Indies and invading South East Asia using their Army and powerful Navy was far easier than taking on the Soviet Armies again in Siberia in a winter campaign.

The only hindrances to securing the oil wells of the Dutch East Indies and transporting that oil back to Japan using the ocean route was the United States Pacific fleet and the Royal Navy in the Far East.

The Japanese attack on Pearl Harbor on Dec 7th 1941 was a knock out blow meant to disable the US fleet and make Japan the dominant Naval power in the Eastern Pacific so that resources from the Philippines, Dutch East Indies and British Malaya could come under the control of the Empire of Japan after their army had taken over these countries and tin, oil, rubber and other raw materials needed for the Japanese industries could easily be transported to Japan using the sea route.

The Japanese air force immediately struck mortal blows at the Royal Navy also in the Far East by sinking two of Britain’s largest battleships: The Prince of Wales and Repulse off Kuantan in the South China Sea on December 10th 1941, before they embarked on their lightning conquest of British Malaya and the Dutch East Indies.

Prince of Wales and Repulse were the first capital ships to be sunk solely by naval - air power on the open sea.