The initial composition of the USSR was determined on the basis that, by the end of the Civil War, the power of the Bolsheviks had been established in several regions of the former Russian Empire. This created certain prerequisites for combining several regions into a single state. The Union of Soviet Socialist Republics was formed on 30/12/1922, when the All-Union Congress approved the agreement on the formation of this state, signed on 29/12/1922.
The first composition of the USSR included the RSFSR, Belarus, Ukraine, and the republics of Transcaucasia (Armenia, Azerbaijan, Georgia). All of them were considered independent and theoretically could leave the union at any moment. In 1924, Uzbekistan and Turkmenistan joined the aforementioned republics, and Tajikistan in 1929.
The territories of present-day Kazakhstan since the 18th century were part of the Russian Empire on an informal basis. However, the state as such was not there. The social system was represented by individual tribes (hordes). In 1936, the territory of Kazakhstan became part of the USSR in the format of the Kazakh Autonomous Soviet Socialist Republic. At the same time, the lands of Kyrgyzstan joined the union.
The path of the other republics to the USSR was longer and less simple. In 1940, Moldova (Bessarabia), which was part of Romania, was transferred to the USSR after the Molotov-Ribentrop Pact was executed. In the same year, the Lithuanian Seimas decided to join this state to the USSR, and the Estonian parliament adopted a declaration on the republic ’s joining the union. Latvia was annexed to the union at the same time.
Thus, it can be said which republics were part of the USSR at the beginning of World War II - Ukrainian, Uzbek, Turkmen, Tajik, Russian, Moldavian, Lithuanian, Latvian, Kyrgyz, Kazakh, Estonian, Belarusian, Armenian and Azerbaijani.
All of them constituted a powerful state that won the Second World War, occupying one sixth of the land, on the territory of which almost all climatic zones, natural resources and various cultures were represented. The USSR actively promoted communist ideas in all parts of the globe and many peoples recall the cooperation of that period as a time without internecine wars, but with the implementation of active construction, the flourishing of education, construction and culture.
The countries that were part of the USSR took advantage of the right to withdraw from the association in 1990-1991 with the formation of 15 states. As time has shown, this decision, partly due to the economic decline caused by the artificial drop in oil prices, was most likely a mistake. As a state of the USSR, it was a well-functioning economic system that collapsed in the first place, causing even greater poverty in the territory of scattered states and a number of wars in which many people died.
Today, attempts are being made to close cooperation between the former republics of the collapsed empire - a structure has been created as a community of independent states and a customs union, which includes Russia, the Republic of Belarus and the Republic of Kazakhstan.