Background. The demand for a Constituent Assembly was a long-standing demand of the democratic and popular movements in Tsarist Russia. In the later phase of the February Revolution, Tsar Nicolas II abdicated on March 2, 1917. The Russian Provisional Government was formed and pledged to carry through with holding elections for a Constituent Assembly. . …

In response, the Estonian SSR was formally incorporated into the Soviet Union on 9 August 1940, and nominally became the 16th constituent republic of the USSR. (On 16 July 1956, the Karelo-Finnish SSR was demoted to the Karelian ASSR ; from then on until 1991, the Estonian SSR was considered the 15th constituent republic.)