Key point: World War II could have ended very differently if Russia and Japan continued fighting.

This is a story of a battle that was, and a war that wasn't.

Between 1938 and 1939, the Soviet Union and the Japanese Empire fought a series of clashes along the border between Japanese-occupied Manchuria, Russian-controlled Mongolia and the Siberian frontier near Russia's vital Pacific port of Vladivostok.

The prizes were the rich resources of Manchuria, and beyond that, which of the two would be the dominant power in Northeast Asia. But even more important was the ultimate outcome of the Manchurian battles, which culminated in Pearl Harbor and the Pacific War between Japan and the United States.

It might be hard to believe that all this began with a few insignificant hills and steppe. Yet both sides had tangled before. In the Russo-Japanese War of 1904-1905, the new Japanese Empire—dismissed by the Tsar's forces as racially inferior Asiatics—sank the Russian navy, outfought the Russian army and seized the strategically important harbor of Port Arthur (which the Russians themselves had previously extorted from China). During the Russian Civil War in 1919, Japan sent 70,000 troops to support the anti-Communist White Army. The Imperial Japanese forces nearly annexed Siberia before withdrawing.

There was little love lost between either side, especially in the ultra-militaristic atmosphere of the 1930s. Japan lurched towards fascism while Stalin bulked up Soviet industrial and military power for the inevitable clash with capitalism. Indeed, the Russo-Japanese conflict was in some ways a battle of mirror images. Whether it meant dying for Stalin or the Emperor, both sides cared nothing for how many of their men perished on the battlefield.

The fuse was first lit at the beginning of the 1930s, when Japan's aggressive Kwantung Army—on its own initiative—occupied China's Manchurian territory in 1931, creating a disputed 3,000-mile frontier between Japan and Russia.

The first serious clash of arms erupted during the Changfukeng Incident (known to the Russians as the Battle of Lake Khasan) in July 1938, when a Japanese division attacked Soviet troops on a disputed hill near Vladivostok. After an attack and counterattack that together cost both sides more than 4,000 casualties, the Japanese withdrew.

Lake Khasan demonstrated the strengths and weaknesses of both sides. The Soviets had superior firepower and many more tanks, but with its leadership decimated by Stalin's purges, the Red Army was rigid and its morale fragile. Lacking the armor and artillery firepower of its more industrialized rivals like the Soviet Union, the Japanese relied on spirit and the will to win at all costs. At first, it seemed like the Japanese knew best. The Soviets eventually deployed 350 tanks, but nearly a hundred were destroyed or damaged by Japanese anti-tank teams. At one point, a Japanese bayonet charge had routed Soviet defenders, reinforcing the Imperial Japanese Army's belief that determined men could beat machines.

With neither side eager to start an all-out war, a ceasefire was arranged. And then nearly a year later, the real test of arms came. It began in May 1939 with a clash of puppets, as a few cavalrymen belonging to Russia's Outer Mongolia satellite entered disputed territory near the village of Nomonhan (the Russians called it the Battle of Khalkin Gol), only to be ejected by cavalry from the Japanese-organized Manchuoko army. When the Mongolian cavalry returned, the Kwantung Army decided to teach them a lesson by sending in the 23rd Infantry Division backed by 70 tanks.

The Soviets responded with attacks by 500 tanks and armored cars, a mighty force but unaccompanied by infantry. "The unsupported Soviet tanks and armored cars rolled forward and did blunt the Japanese offensive," writes Edward Drea in a U.S. Army monograph on Japanese forces in the battle. "Japanese troops destroyed at least 120 Soviet tanks or armored cars with Molotov cocktails, 37-mm antitank guns and antitank mines."

The battle lines settled into small patrols and raids, but unfortunately for Japan, there arrived a new Soviet commander named Georgy Zhukov, soon to be the nemesis of Hitler's armies. Just as he later did to the Germans, Zhukov unleashed a mechanized blitzkrieg of infantry, armor and artillery that encircled and destroyed the 23rd Division before a ceasefire was declared.  The Japanese suffered 17,000 casualties while the Soviets lost 10,000 men.

Tactically, the battle highlighted the weaknesses of an infantry-centric army fighting a conventional battle against mechanized forces in open terrain. It also broke the comforting myth that morale beats firepower (though the reverse isn't always true, either, as the U.S. discovered in Vietnam). "Doctrine could only carry it so far when there were too few Japanese tanks and too few artillery pieces to influence decisively the outcome of the battle," Drea writes. "This left the Japanese infantrymen armed with gasoline-filled bottles to face counterattacks by Soviet tanks and infantry supported by artillery."

For all its bluster, Japan had been a taught a lesson it would not forget. Or, rather, the tactical lessons would be forgotten five years later, when Japanese soldiers again had to turn themselves into human anti-tank mines in a vain attempt to defeat American Sherman tanks.

But the bigger consequence to history was what didn't happen. In the summer of 1941, as the Soviet Union seemed about to collapse under the Nazi blitzkrieg, Japan had a choice. It could strike north and seize Siberia, while the bulk of the Red Army fought in Europe. Or it could strike south, at the resource-abundant Pacific colonies of the British, Dutch and Americans.

"If successful, a limited Japanese-Soviet war in the Soviet Far East might have tipped the balance in European Russia to Nazi Germany," Drea told The National Interest.

There were many reasons why Japan chose the southern option, including the U.S. oil embargo and the helplessness of Europe's Pacific colonies while their mother countries were occupied by the Nazis. However, another reason for not attacking north was the memory of what happened at Nomonhan.

Stalin was free to transfer his elite Siberian troops from the Far East to Europe, where they threw back Hitler's panzers from the gates of Moscow in December 1941. And Japan chose the Pacific option, thus unleashing a war with America that doomed the Japanese Empire.

Note: The definitive book on Nomonhan/Khalkin Gol remains Alvin Cox's "Nomonhan: Japan Against Russia, 1939."

Michael Peck, a frequent contributor to TNI, is a defense and historical writer based in Oregon. His work has appeared in Foreign Policy, WarIsBoring and many other publications. He can be found on Twitter and Facebook. This first appeared several years ago and is being republished due to reader interest.

Image: Wikipedia.