Artsakh in the Soviet Era

No sooner had Artsakh recovered from such a blow than the communists came to the South Caucasus. The Sovietization of the territories of the Democratic Republic of Azerbaijan and, later, the Republic of Armenia and the disputed territory of Artsakh began.
From the letters of the Karabakh District RevCom of Asad Garayev to the Gerusi District RevCom:

July 19, 1920

"Your old policy was deeply mistaken: i.e., the occupation of Karabakh and Zangezur by troops. We know that our troops have been defeated and retreated, but today our money is doing wonders instead of troops. Again and again I repeat my advice - don't spare any amount, increase salaries, give bonuses and all the things they want. The government decided to allocate 200 million rubles for annexing Karabakh and Zangezur to Azerbaijan".

July 21, 1920

"Still 90% of the Zangezur villages have not yet been disarmed. This is sad. But even more unfortunate is the fact that the Armenians of Zangezur have not yet been beheaded. Its intellectuals and military chiefs still remain in the villages. Make sure that all prominent and necessary Armenians are arrested. Leave humanity behind. You cannot create a state, conquer countries with it... In the famous places rich in warriors, in order to weaken Armenians, kill one Russian soldier and blame it on Armenians. Do you know what the Russians will do to them? Do not leave any decent person or wealth in Zangezur, so that this cursed tribe (Armenians) could no longer rise on their feet".
During the Sovietization era, Karabakh's situation remained in limbo for some time, and Armenia and Azerbaijan continued to claim control over the territory. The issue was finally resolved at the plenum of the Caucasian Bureau on July 4, 1921, which decided to incorporate Karabakh into the Armenian Soviet Republic.

But the very next day with Stalin's signature and under the pressure of the Azerbaijani leader Narimanov, another decision was made — this time without discussion or voting — to include Karabakh in the status of an autonomous region within Soviet Azerbaijan.
Nariman Narimanov, Chairman of the Council of People's Commissars of the Azerbaijan SSR and Joseph Stalin

The borders were also determined at Baku's discretion, resulting in a border that completely cut Artsakh off from Soviet Armenia and turned it into an enclave within Azerbaijan, with a number of Armenian-populated Karabakh territories not included in the NKAO.
One of the main Soviet figures of that era, Sergo Ordzhonikidze, shortly before his death, spoke about his impressions after the Communists' arrival in Karabakh:

"I still remember with horror the picture we saw in Shusha in May 1920. The most beautiful Armenian city was destroyed, ruined and razed to the ground. and in the wells we saw the corpses of women and children".
Conclusion: Sovietized Azerbaijan continued the nationalist policy towards Karabakh and carried it through to the end, while reducing the territory of Nagorno-Karabakh and making it an enclave, thereby securing itself for the future.

The collapse of the USSR and the formation of two countries on the territory of Soviet Azerbaijan

The provision on the right of the Union Republics to secede from the USSR was an important legal component included in the Constitution of the USSR. In this context, the latter Constitution, adopted on 7 October 1977, is no exception.
According to Article 3 of Law No. 1409-I

"In a Union Republic with autonomous republics, autonomous regions and autonomous districts, a referendum shall be held separately for each autonomy. The peoples of autonomous republics and autonomous formations shall retain the right to independently decide the question of staying in the Soviet Union or in the seceding Union republic, as well as to raise the question of their state-legal status. In a Union Republic, in the territory of which there are places of compact residence of national groups that make up the majority of the population of a given locality, the results of voting in these localities are taken into account separately when determining the results of the referendum".
It was this article that served as a basis for further decisions on the proclamation of Artsakh's independence on September 2, 1991 and on the referendum on December 10, 1991.

Note that the referendum was held under constant shelling of Armenian settlements with various types of weapons, which did not prevent citizens from taking part in it. It should also be emphasized that the Azerbaijanis did not participate in the referendum, but considering that Armenians were the majority of the NKR population (over 75%), it becomes clear, that their non-participation in any case could not affect the results of the referendum.
Conclusions: Thus, we can confidently assert that the people of Artsakh exercised their right to self-determination in strict compliance with the then USSR Constitution and international law.
The people of Artsakh at a rally in 1988 demanding to join Armenia