Following the establishment of Soviet power in Azerbaijan in April 1920, in Armenia in November 1920, and in Georgia in February 1921, Soviet Russia began implementing a plan to unite the three Soviet republics of the South Caucasus into a single union, subsequently annexing this union to Soviet Russia. In 1921, for the first time, resolutions were adopted to abolish customs and border checkpoints between the Transcaucasian republics, to consolidate foreign trade institutions, and to unify railways.

This preliminary economic consolidation of the Transcaucasian republics marked a new phase towards their full convergence. Essentially, under the guise of state-political unification, groundwork was laid for the next step in curtailing their independence. The plenum of the Caucasian Bureau of the Central Committee of the RCP(b), held on November 3, 1921, in Baku with the participation of the secretary of the Central Committee of the RCP(b), V.M. Molotov, members of the Central Committee of the Communist Parties of Azerbaijan, Georgia, and Armenia, having reviewed reports from G.K. Ordzhonikidze on the federation of the Transcaucasian republics and Sh.Z. Eliava on the Union Treaty project, resolved to establish a federative union among the republics primarily in the military, economic, financial, and foreign trade spheres. It was decided to create an administrative-economic center for theTranscaucasian republics – the Union Council and to form a commission to develop the union treaty project. However, a group of leaders from Georgia and Azerbaijan opposed the federation of the Transcaucasian republics. Despite some members' objections to such a union, the party bodies approved the "Union Treaty of the Soviet Socialist Republics of Azerbaijan, Georgia, and Armenia." A group of party figures, led by P.G. Mdivani in Georgia, R.A. Akhundov, and M.D. Huseynov in Azerbaijan, argued that it was premature to create a federation.

By the end of 1921 and beginning of 1922, elections to the Soviets were completed in all Transcaucasian republics, which supported the federation's creation. The First Congress of Communists of Transcaucasia, held in Tbilisi from February 18 to 22, 1922, aimed at unifying communist organizations of Transcaucasia under a single party leadership to "centralize the management of all Transcaucasia in the hands of the Center."

The First Congress of Communist Organizations of Transcaucasia approved the "Union Treaty of the Azerbaijani, Armenian, and Georgian SSRs" presented by the commission, as well as the "Regulation on the Supreme Economic Council."

On March 3, 1922, the third session of the Central Executive Committee of Azerbaijan approved the federation's creation and the Regulation on the Federative Union of Transcaucasian Republics. The Central Executive Committee of the Azerbaijani SSR confirmed a delegation of 25 delegates with decisive votes and 3 with advisory votes for the Transcaucasian plenipotentiary conference. The delegation included S.M. Efendiev, M.N. Israfilbekov (Kadirli), V.G. Yegorov, S.D. Yakubov, N.N. Narimanov, N.G. Poltoratsky, E.I. Rodionov, M. Shahbazov, among others.

On March 7-8, 1922, the plenum of the Central Committee of the CP(b) of Azerbaijan discussed the union government's composition and approved the proposal to establish its Presidium, including N.N. Narimanov, M.F. Myasnikov, and a representative of the Georgian SSR.
    
On March 11, 1922, a plenipotentiary conference of representatives from the Central Executive Committees of Azerbaijan, Armenia, and Georgia was held in Tiflis. The conference, the highest authority with a one-year mandate, was to be convened at least three times a year. It created its executive body – the Union Council, its Presidium composed of three members (one from each republic), and the Supreme Economic Council. The conference also confirmed the nominations for the chairman of the Supreme Economic Council and the chief of the Transcaucasian Railway.

On March 12, 1922, the Plenipotentiary Conference adopted the Union Treaty, establishing the Federative Union of Socialist Soviet Republics of Transcaucasia (FUSSRT). The Union Treaty declared: The Plenipotentiary Conference of the socialist Soviet republics of Azerbaijan, Armenia, and Georgia, guided by the Great Proletarian Revolution's proclaimed right of nations to self-determination, acknowledging the independence and sovereignty of each contracting party, and recognizing the necessity to unite their forces for defense and economic construction, resolved that the socialist Soviet republics of Azerbaijan, Armenia, and Georgia henceforth enter into a close military, political, and economic union.
    
On April 28, 1922, the Second All-Azerbaijani Congress of Soviets ratified the Union Treaty.
   
On December 13, 1922, the 1st Transcaucasian Congress of Soviets (Baku) transformed the FUSSRT into the Transcaucasian Socialist Federative Soviet Republic and adopted the Constitution of the TSFSR.
   
On December 30, 1922, at the First All-Union Congress of Soviets, representatives of the RSFSR, Ukrainian, and Belarusian Soviet Socialist Republics, along with the Transcaucasian Federation, signed the Declaration on the Formation of the USSR and the Union Treaty.
   
This act marked the end of Azerbaijan's independence. Although the Azerbaijani SSR retained several state symbols adapted to those of the USSR - flag, coat of arms, anthem, and constitution - it lost its status as a subject of international law and legally became a colony of Bolshevik Russia.

Recommended literature:

1. Hacıyev, Hacı. İstiqlalın əzablı yolu: Azərbaycan Demokratik Respublikası tarixinin bəzi səhifələri /H. Hacıyev; red. M. Səfərli; Azərbaycan Jurnalistlər İttifaqı. - Bakı: Azərbaycan Jurnalistlər İttifaqı, 1991. - 32 s.
2. Азәрбајҹан тарихи : 7 ҹидддә / АМЕА А.А. Бакыханов адына Тарих Институту. - ISBN 5-8066-1256-2. VI ҹилд : Апрел 1920 - ијун 1941 / мәс’ул ред. Ҹ. Б. Гулијев [et al.]. - Бакы : Елм, 2000. - 568 с.
3. Каземзаде, Фируз. Борьба за Закавказье: 1917-1921 / Ф. Каземзаде ; пер. А. Умаевой ; Институт Стратегических Исследований Кавказа. - Стокгольм : CA&CC Press, 2010. - 328 с.