Besides national republics, oblasts, and okrugs, several hundred national districts (with populations between 10,000 and 50,000) and several thousand national townships (population 500 to 5,000) were established. In some cases this policy required voluntary or forced resettlement in both directions to create a compact population. Ethnic left immigration and the return of non-Russian émigrés to the Soviet Union during the New Economic Policy, albeit perceived as an easy cover for espionage, were not discouraged and proceeded quite actively, contributing to nation-building.