Mass operations of the NKVD were carried out during the Great Purge and targeted specific categories of people. As a rule, they were carried out according to the corresponding order of the People's Commissar of Internal Affairs Nikolai Yezhov.
The operations of this type in this period targeted "foreign" ethnicities (ethnicities with cross-border ties to foreign nation-states), unlike nationally-targeted repressions during World War II.
On November 17, 1938 a joint decree of Sovnarkom USSR and Central Committee of Communist Party of the Soviet Union and the subsequent order of the NKVD undersigned by Lavrentiy Beria cancelled most of NKVD orders of this type (but not all, see, e.g., NKVD Order no. 00689) and suspended implementation of death sentences, signifying the end of the Great Purge ("Yezhovshchina").