 After the failure of the Tatarbunary Uprising in 1924, the Moldavian Autonomous Soviet Socialist Republic (Moldavian ASSR) was formed by Soviet Russia within the territory of the Ukrainian SSR, in Transnistria region.In August 1939, the Molotov–Ribbentrop Pact and its secret additional protocol were signed, by which Nazi Germany recognized Bessarabia as being within the Soviet sphere of influence, which led the latter to actively revive its claim to the region.On 28 June 1940, the Soviet Union issued an ultimatum to Romania requesting the cession of Bessarabia and northern Bukovina, with which Romania complied the following day.