Despite the 1920 treaty of non-aggression signed between Bolshevik Russia and Georgia, Soviet Russia’s 11th Red Army invaded Georgia on February 11 1921, and marched on Tbilisi. Almost simultaneously, 9th (Kuban) Army entered Abkhazia on February 19. Supported by the local pro-Bolshevik guerrillas, the Soviet troops took control of most of Abkhazia in a series of battles from February 23 to March 7, and proceeded into the neighbouring region of Mingrelia.
On March 4, Soviet power was established in Sokhumi, with the formation of the Abkhazian Soviet Socialist Republic (Abkhazian SSR), allegedly recognized by the newly established Communist regime of the Georgian SSR on May 21. On December 16, however, Abkhazia signed a special "union treaty" delegating some of its sovereign powers to Soviet Georgia. Abkhazia and Georgia together entered the Transcaucasian SFSR on December 13 1922 and on 30 December joined the Union of Soviet Socialist Republics. Abkhazia's ambiguous status of Union Republic was written into that republic's April 1, 1925 constitution. Paradoxically, an earlier reference to Abkhazia as an autonomous republic in the 1924 Soviet Constitution remained unratified until 1931 when Abkhazia's status was reduced to an Autonomous Soviet Socialist Republic (ASSR) within the Georgian SSR. Except for a few nobles, the Abkhaz did not participate in the 1924 August Uprising in Georgia, a last desperate attempt to restore the independence of Georgia from the Soviet Union.
During the Stalin years, a purge was carried out against Communist Party officials and intelligentsia of Abkhaz provenance on the orders of Lavrentiy Beria, then-the Party Secretary in Transcaucasus and himself a native of Abkhazia, in order to break a resistance to forced collectivization of land. The Abkhaz party leader Lakoba suddenly died shortly after his visit to Beria in Tbilisi in December 1936. There was a strong suspicion that he was poisoned by Beria who declared Lakoba an "enemy of the people" posthumously. Stalin’s five-year plans also resulted in the resettlement of many Russians, Armenians, and Greeks into Abkhazia to work in the growing agricultural sector.
Abkhaz were given a greater role in the governance of the republic after Beria’s death in 1953. As in most of the smaller autonomous republics, the Soviet government encouraged the development of culture and particularly of literature. A new script, based on Cyrillic, was devised for Abkhaz, Abkhaz schools opened; and administration put largely in the Abkhaz hands. Ethnic quotas were established for certain bureaucratic posts, giving the Abkhaz a degree of political power that was disproportionate to their minority status in the republic. This was interpreted by some as a "divide and rule" policy whereby local elites were given a share in power in exchange for support for the Soviet regime. In Abkhazia as elsewhere, it led to other ethnic groups — in this case, the Georgians — resenting unfair discrimination and disregard of the rights of majority, thereby stoking ethnic discord in the republic.
The following three decades were marked by attempts of the Abkhaz Communists to make the autonomous structures more Abkhaz, but their efforts constantly met resistance from the Georgians. Abkhaz ultra-nationalists attempted on several occasions, most notably in 1978, to convince Moscow the autonomous republic to be transferred from Georgia to the Russian SFSR. That year, the Abkhaz organized a series of indoor and outdoor rallies in response to the mass demonstrations of Georgians who succeeded in winning for their language a constitutional status of the official language of the Georgian SSR. Although the Abkhaz request of the secession from Georgia was rejected Moscow and Tbilisi responded with serious economic and cultural concessions, appropriating an extra 500 millions rubles over seven years for the development of infrastructure, and cultural projects such as the foundation of the Abkhaz State University (with Abkhaz, Georgian, and Russian sectors), a State Folk Ensemble in Sokhumi, and Abkhaz-language television broadcasting. Even though these concessions eased tensions only partially, they made Abkhazia one of the most prosperous regions of Georgia, the wealthiest Soviet republic of that time. The favourable geographic and climatic conditions were successfully exploited to make Abkhazia a destination for hundreds of thousands of tourists, gaining for the region a reputation of "Soviet Riviera."