The Moldavian Soviet Socialist Republic from which the PMSSR seceded was created in 1940 following the Soviet annexation of territory belonging to the Kingdom of Romania. When Bessarabia was ceded to the Soviet Union as a result of an ultimatum, it was combined with a strip of land on the left bank of the Dniester which had formed the nucleus of a Moldavian Autonomous Soviet Socialist Republic (MASSR), an autonomous republic of the Ukrainian Soviet Socialist Republic with Tiraspol as its executive capital, throughout the interwar period.