Soviet-Japanese Neutrality Pact

Background: two empires share a border

By the mid-1930s the creation of Manchukuo and Japan's invasion of China brought the Soviet Union and the Empire of Japan into direct territorial contact. The USSR needed to stabilise its eastern frontier while facing the prospect of war with Germany, and Japan, bogged down in China and with rapidly worsening relations with the United States, wanted "a safety valve for Manchukuo's northern border." The Kwantung Army's crushing defeat by the Red Army at Khalkhin Gol in May 1939 had already destroyed the Japanese army's Strike North faction, and negotiations proceeded on that basis. On 13 April 1941 the pact was signed in Moscow by Molotov for the USSR and Foreign Minister Yosuke Matsuoka and Ambassador Yoshitsugu Tatekawa for Japan.

Signed in Moscow on 13 April 1941, the pact's preamble recorded that "the Presidium of the Supreme Soviet of the USSR and His Majesty the Emperor of Japan," guided by a desire to strengthen peaceful and friendly relations, had decided to conclude a neutrality pact and had appointed Molotov as Soviet representative and Matsuoka and Lieutenant General Tatekawa as Japan's.

What the pact said

Article one bound both parties to maintain peaceful and friendly relations and to respect each other's territorial integrity and inviolability. Article two was the core obligation: should one party become the object of hostilities by a third power or several, the other would remain neutral for the duration of the conflict. Article three provided that the pact entered into force on ratification and remained valid for five years, and would be automatically renewed for another five unless either party denounced it one year before expiry. Article four required ratification as soon as possible and the exchange of instruments in Tokyo.

An attached declaration, signed the same day, pledged the USSR to respect the territorial integrity and inviolability of Manchukuo and Japan the same for the Mongolian People's Republic.

1941: the pact in a world war

The signing halted Soviet aid to the Nationalist government in China. When Germany invaded the Soviet Union two months later, Japan, although a signatory of the Tripartite Pact, kept the neutrality pact and expanded southward instead. Japanese army and navy leaders resolved two days after the German invasion "not to intervene in the German-Soviet war for the time being." Khalkhin Gol and the pact were the basis for that decision. The choice in turn allowed the USSR to shift Far Eastern forces westward while Japan turned toward Pearl Harbor. For most of World War II the two nations fought each other's allies but never each other.

1945: denunciation and war

At the Yalta Conference in February 1945 Stalin secretly agreed to enter the war against Japan within three months of Germany's surrender, in exchange for Anglo-American recognition of Soviet territorial claims in Asia. On 5 April 1945 the Soviet Union notified the Japanese government of its denunciation, citing "the right of denunciation one year before the lapse of the five-year period" under Article Three. The pact remained valid until 13 April 1946, but the wording suggested the USSR wished it to lapse immediately. When Ambassador Naotake Sato pressed him, Molotov assured him the treaty would remain in force until April 1946. Germany's surrender on 8–9 May 1945 started the secret three-month countdown, the Soviet invasion of Manchuria began on 9 August, and the declaration of war followed nearly six hours later. During the invasion Soviet forces took Manchukuo, Mengjiang (Inner Mongolia), and northern Korea.