張鼓峰事件
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 War II.