Establishment of Soviet Rule
The establishment of Soviet rule in the Transcaucasus led to a new political order. After the proclamation of Soviet Azerbaijan in 1920, an agreement between Soviet Russia and the Republic of Armenia, allowed the Russian army to temporarily take control of Nagorno Karabakh until a peaceful settlement to the conflict could be agreed upon.
However, immediately after the establishment of the Soviet Rule in Armenia, the Revkom (Revolutionary Committee - the Bolsheviks' main governing body at the time) of Azerbaijan declared the "disputed territories", namely Nagorno Karabakh, Zangezur and Nakhichevan as inseparable parts of Armenia.
Based on the withdrawal of Azerbaijan's claims on the "disputed territories" and the agreement between the Governments of Armenia and Azerbaijan, Armenia declared Nagorno Karabakh an inseparable part of its country on June 1921. The text of the Decree of the Armenian Government was published in the Armenian and Azerbaijani press (Bakinsky Rabochy - organ of the Central Committee of the Communist Party of Azerbaijan - June 22, 1921.). This act signified the last legal act in terms of international law regarding Nagorno Karabakh during the Soviet rule in the Transcaucasus.
The international community and Russia welcomed this act, which was reflected in a resolution of the League of Nations Assembly, in the March 4, 1921 Reference Note of the League of Nations Secretary to its member-states, and in the 1920-1921 Annual Report of the People's Commissariat (Ministry) of Soviet Russia's Foreign Affairs to its highest governing body - the 19th Congress of Soviets.
However, the Bolshevik Leadership of Russia soon changed its attitude on the problem of "disputed territories," including Nagorno Karabakh. This political move was undertaken in consideration of the policy of assisting the "world-wide communist revolution", in which Turkey, having ethnic links with Azerbaijan, was entrusted the role of "beacon of revolution in the East".
Following Moscow's orders, the Azerbaijani leadership renewed its claims on Nagorno Karabakh. The Plenum of the Caucasus Bureau of the Russian Communist Party of Bolsheviks' (Kavbureau) ignored the decision of the League of Nations and rejected the referendum. In procedural violation, it adopted a decision to separate Nagorno Karabakh from Armenia and annex it to Soviet Azerbaijan, promising to establish a national autonomy on its Armenian-populated territories. However, Azerbaijan delayed granting autonomy to Nagorno Karabakh. After a two-year armed struggle and at the Russian Communist Party's insistence, the Central Committee of the Communist Party of Azerbaijan, granted a small part of Karabakh the right to an autonomous oblast (a type of nation-state formation in the USSR Constitution). This became known as the Nagorno Karabakh Autonomous Oblast (NKAO). Even with this autonomous region, Nagorno Karabakh was further divided as the other parts not included in the oblast were incorporated into the regions of Soviet Azerbaijan, thus enabling physical and geographical separation of the Armenian populated areas from Armenia.
Thus, a large portion of the territory recognized as "disputed" by the League of Nations was directly annexed to Azerbaijan, with the bulk of Nagorno Karabakh left out of the autonomous oblast (Gyulistan, Kelbajar, Gharakhat aka Dashkesan, Lachin, Shamkhor, etc.).