Soviet–Japanese Neutrality Pact

The Soviet–Japanese Neutrality Pact (日ソ中立条約, Nisso Chūritsu Jōyaku), also known as the Japanese–Soviet Non-aggression Pact (日ソ不可侵条約, Nisso Fukashin Jōyaku), was a non-aggression pact between the Soviet Union and the Empire of Japan signed on April 13, 1941, two years after the conclusion of the Soviet-Japanese Border War. The agreement meant that for most of World War II, the two nations fought against each other's allies but not against each other.

Source: Wikipedia — Soviet–Japanese Neutrality Pact (CC BY-SA 4.0)