The Russian Empire had the largest Jewish population in the world in the 19th and early 20th centuries and the majority of them were Ashkenazi Jews. Large numbers of them remained even after 2 million of them departed for other countries prior to the formation of the Soviet Union. While thousands of Jews migrated to Birobidzhan, the hardship and isolation caused most to leave. In 1939 the Jewish population made up less than twenty percent of the overall population. Shortly after World War II, the Jewish population in the region reached its peak of about 30,000. As of the mid-2010s, only about 2,000 Jews remain in the region, making up about one half of a percent of the population.