While Germany was massing its tanks for the run on Poland, Russia and China were battling it out in Asia. Their first border war was the Battle of Lake Khasan, which lasted from July to August 1938; their second was the Battle of Khalkhin Gol, in the summer of 1939. Then both sides realized there were larger forces at play. The Soviets cast a wary eye on the Polish blitzkrieg, while Japan needed to secure its western border to focus on the pacific. The Russo-Japanese neutrality pact satisfied both conditions.

On this day, April 13, in 1941, Soviet Foreign Minister Vyacheslav Mikhailovich Molotov (the same one who signed the non-aggression pact with Germany a year earlier) and the Japanese ambassador to Russia signed the neutrality treaty.

After Germany violated the non-aggression pact with Russia and invaded in 1941, Stalin feared a second front invasion from Japan to the east. Japan, however, had all its military power committed to the Pacific war. It was Russia who would, in fact, violate the pact: in 1945, near the end of WW II, when, at the behest of the Allies, they invaded Japanese-held Manchuria.