in 1905, Japan took control of southern Sakhalin Island and the Kuril Islands. In 1920, The Bolsheviks took over northern Sakhalin, but within months the Japanese captured it and began to exploit its oil, coal, and other resources. Under international pressure, the northern district of Sakhalin was transferred to the Soviet Union in 1925, but the Japanese retained a concession there. In 1945 the Soviets seized all of Sakhalin and the Kuril Islands. 1925–1930: Quiet cooperation The early years following the establishment of diplomatic relation were characterized by calm, which was mainly the result of the partial restraint in the expansionist policies of the Japanese Empire prior to 1931, as well as the Soviet need to maintain trade and the temporary deterioration in Sino-Soviet relations around the period of the Sino-Soviet war in 1929. Already in 1925, immediately following the establishment of relations, the Japanese government withdrew its forces from the northern part of Sakhalin, captured by the Japanese army during the Siberian intervention. An important step during this period was the conclusion on January 23, 1928, of a Soviet-Japanese Fishery agreement, which permitted Japanese nationals to fish in the waters of the Pacific Ocean adjacent to the Soviet coastline. Ratifications were exchanged in Tokyo on May 23, 1928. The agreement was registered in League of Nations Treaty Series on September 5, 1928. 1930–1945: Deteriorating relations and war Beginning in 1930 amid deteriorating relations with Poland, Joseph Stalin became concerned about the possibility of a two-front war with Poland and Japan. In particular, he feared that Japan would encourage nomads in Soviet Central Asia to rebel against the Soviet Union's forced sedentarization policies. After the Japanese invasion of Manchuria and the establishment of the puppet state of Manchukuo in 1932, Japan turned its military interests to Soviet territories. Soviet-Japanese relations sharply deteriorated after 1936. This stemmed from the conclusion of the Anti-Comintern Pact between Japan and Nazi Germany in November 1936, which was designed as a defense against international communism. The first major Soviet-Japanese border incident, the Battle of Lake Khasan (1938), happened in Primorye, not far from Vladivostok. Conflicts between the Japanese and the Soviets frequently happened on the border of Manchuria, escalating into an undeclared border war which was decided in the Battle of Khalkhin Gol (1939), which took place at the Mongolian-Manchurian border. The Soviet Union won decisively, and deterred Japan from any further aggression during World