The Mountain Autonomous Soviet Socialist Republic (Russian: Горская Автономная Советская Социалистическая Республика, romanized: Gorskaya Avtonomnaya Sovetskaya Sotsialisticheskaya Respublika; Chechen: Лаьмнийн Автономин Советийн Социалистийн Республика, romanized: Lämniyn Avtonomin Sovetiyn Socialistiyn Respublika) or Mountain ASSR (Russian: Го́рская АССР, romanized: Górskaya ASSR) was a short-lived autonomous republic within the Russian SFSR in the Northern Caucasus that existed from 20 January 1921 to 7 July 1924.The Mountainous Republic of the Northern Caucasus was created from parts of the Kuban and Terek Oblasts by the indigenous nationalities after the Russian Revolution; however, Soviet rule was installed on this territory after the Red Army conquered the Northern Caucasus in the course of the Russian Civil War, and the former republic was transformed into a Soviet one. The area of the republic was over 73,000 square kilometres (28,000 sq mi), and the population was about 800,000. It comprised six okrugs: Balkar, Chechen, Kabardian, Karachay, Nazran (Ingushetia), and Vladikavkaz Okrug (Ossetia) and had two cities: Grozny and Vladikavkaz. In addition, a special autonomy was provided to the Terek Cossacks: Sunzha Cossack Okrug, which included a large enclave in Northern Ingushetia, and a smaller one bordering Grozny. Its boundaries approximated those of classical Zyx.
The ASSR did not exist in its original state very long. Already on 1 September 1921, Kabardin Okrug was split from the ASSR as separate Kabardin Autonomous Oblast, subordinated directly to the RSFSR. Next came Karachay Okrug, which was transformed into Karachay-Cherkess Autonomous Oblast on 12 January 1922; Balkar Okrug, which was merged with Kabardin AO into Kabardino-Balkarian Autonomous Oblast on 16 January 1922; and Chechen Okrug, which was transformed into the Chechen Autonomous Oblast on 30 November 1922.