Mongolia: Soviet BT07 tanks and infantry attacking at Khalkhin Gol, 1939

The Battle of Khalkhyn Gol was the decisive engagement of the undeclared SovietÐJapanese Border War fought between the Soviet Union, Mongolia and the Empire of Japan in 1939. The conflict was named after the river Khalkhyn Gol, which passes through the battlefield. In Japan, the decisive battle of the conflict is known as the Nomonhan Incident (Nomonhan Jiken) after a nearby village on the border between Mongolia and Manchuria. The battles resulted in total defeat for the Japanese Sixth Army. Casualty estimates vary widely: Some sources say the Japanese suffered 45,000 or more soldiers killed with Soviet casualties of at least 17,000. The Japanese officially reported 8,440 killed and 8,766 wounded, while the Soviets initially claimed 9,284 total casualties. Although this engagement is little known in the West, it had profound implications on the conduct of World War II. It may be said to be the first decisive battle of World War II, because it determined that the two principal Axis Powers, Germany and Japan, would never geographically link up their areas of control through Russia. The defeat convinced the Imperial General Staff in Tokyo that the policy of the North Strike Group, favoured by the Imperial Japanese Army, which wanted to seize Siberia as far as Lake Baikal for its resources, was untenable. Instead the South Strike Group, favored by the Imperial Japanese Navy, which wanted to seize the resources of Southeast Asia, especially the petroleum and mineral-rich Dutch East Indies, gained ascendancy, leading directly to the attack on Pearl Harbor two and a half years later in December 1941. (Photo by: Pictures From History/Universal Images Group via Getty Images)