Simultaneously with the complication of the situation in Europe, the situation in the Far East continued to worsen. Japan tried to create a vast base for conquering China and the territories of several other states. The position of Japan in relation to the USSR became more and more aggressive and militant.

At the beginning of 1936, in the context of an increased threat of attack on the Mongolian People’s Republic (MPR), the question of concluding an agreement between the governments of Mongolia and the USSR arose. As a result, on March 12, a Soviet-Mongolian protocol on mutual assistance for a period of 10 years was signed in Ulan Bator, which replaced the agreement of 1934. In accordance with the agreement, Soviet troops were deployed on the territory of Mongolia.

Wanting to check the Soviet borders for "strength", on July 29, 1938, Japan, by means of several hundred soldiers, attacked the USSR border post on the hill of Bezymyannaya. The units of the regular troops of the Red Army arrived at the aid of our border guards and knocked out the Japanese who had broken through the border. A few days later, Japan repeated its maneuver, capturing a number of important points in the area of ​​Lake Hassan (Far East). In early August 1938, the troops of the Far Eastern Front (Commander Marshal V.K. Blucher) fought with the enemy, during which the Japanese government offered to begin negotiations.

On August 11, hostilities between the Soviet and Japanese forces were ceased. The casualties of Japanese troops during the battles at Lake Hassan amounted to 500 people killed and 900 wounded. The losses in this two-week conflict on the part of the Red Army turned out to be more significant: 792 people were killed, deceased from wounds and missing and more than 3 thousand wounded and sick.

At the beginning of 1939, the Japanese government headed K. Hiranuma, who represented the fascist-minded groups in the ruling circles of Japan. The military leaders of the “rising sun” country publicly spoke out with threats against the USSR, suggesting to public opinion the idea of ​​the weakness of Soviet troops. In early May 1939, the Japanese General Staff received instructions from the emperor to begin military operations against the Mongolian People's Republic in the area of ​​the Khalkhin Gol River. V.Molotov warned the Japanese ambassador to the USSR that "we will defend the border of the Mongolian People's Republic, by virtue of the mutual assistance agreement concluded between them, as our own border".

In the first days of June 1939, after armed violations of the borders of the Mongolian People's Republic by Japanese forces, it became clear that the goal of Japan was to capture part of Mongolia. The Deputy Commander of the Forces of the Belarusian Military District G. K. Zhukov was summoned to Moscow.

He received instructions from the People's Commissar for Defense K. Ye. Voroshilov to take over the command of the Soviet units in the territory of Mongolia. Assessing the situation on the spot, Zhukov came to the conclusion that by the 57th Special Corps, which by the end of May counted only 5.5 thousand people, the task of defeating the Japanese could not be solved. Soviet troops were strengthened by aviation, tanks, artillery. By the end of hostilities, their numbers amounted to 57 thousand people. In early July, our troops defeated the Japanese on Mount Bain-Tsagan. On August 20, the decisive offensive of units of the Red Army began, which in September ended with a complete defeat of the 6th Japanese Army, which invaded the Mongolian People's Republic.

The news of the conclusion of a non-aggression treaty between the USSR and Germany had a demoralizing effect on Japan. This was a violation of the “Anti-Comintern Pact” and caused an acute crisis in the ruling circles. The Hiranuma government, which built its policy on cooperation with Germany, resigned.

The Soviet command highly appreciated the merits of the Red Army soldiers: 70 people received the title of Hero of the Soviet Union . Among them was the commander of the troops G. K. Zhukov. The famous Golden Pilots S. I. Grinevets, Ya. V. Smushkevich, G. P. Kravchenko were awarded the Second Golden Star.

The loss of the Red Army during the fierce fighting amounted to about 8 thousand people. There were 16 thousand injured and sick. The losses of the Japanese troops exceeded 60 thousand people killed, wounded and captured, 660 aircraft, as well as a significant amount of other military equipment.

In Japan, which found itself in international isolation, more and more voices began to be heard for the normalization of relations with the Soviet Union. In December 1939, negotiations were held between the two countries on the expansion of trade relations. An agreement was signed to extend for one year the fishing agreement in force since 1928. On December 31, a Soviet-Japanese agreement was concluded regarding the final payment by Japan for the Chinese-Eastern Railway.

However, the establishment of economic ties did not mean that Japan abandoned its aggressive plans. In March 1940, a plan of attack on the USSR was prepared and approved by the emperor in the general staff in order to capture the Soviet Primorye.

Under these conditions, Moscow turned out to be interested in normalizing relations with its far-eastern neighbor. After difficult negotiations on April 12, 1941, Foreign Minister of Japan I. Matsuoka was received in the Kremlin by Stalin. On April 13, a neutrality pact between the USSR and Japan was signed. The key provision of this agreement was that “in the event that one of the contracting parties becomes the object of military actions by one or several third powers, the other contracting party will maintain neutrality throughout the conflict”. The contract was concluded for 5 years. He did not remove from the Soviet leadership fears of a possible struggle on two fronts, but still significantly improved the position of the USSR on the eastern and western frontiers.