Between 1937 and 1939, the Soviet Union under Joseph Stalin deported over 200,000 Koreans to Uzbekistan and Kazakhstan, fearing that the Koreans might act as spies for Japan. Many Koreans died on the way in cattle trains due to starvation, illness, or freezing conditions. Soviet authorities purged and executed many community leaders; Koryo-saram were not allowed to travel outside of Central Asia for the next 15 years. Koreans were also not allowed to use the Korean language and its use began to become lost with the involvement of the Koryo-mar dialect and the use of Russian.