The Transnistria Governorate (Romanian: Guvernământul Transnistriei) was a Romanian-administered territory, annexed by the Axis Powers from the Soviet Union during Operation Barbarossa and occupied from 19 August 1941 to 29 January 1944. Limited in the west by the Dniester river (separating it from Bessarabia Governorate) in the east by the Southern Bug river (separating it from the German Reichskommissariat Ukraine), and in the south by the Black Sea, it comprised the present-day region of Transnistria (which compared to the World War II whole is only a small strip along the bank of the Dniester) and territories further east (modern Odessa Oblast eastward of the Dniester and southern Vinnytsia Oblast), including the Black Sea port of Odessa, which became the administrative capital of Transnistria during World War II.
In World War II, Romania, persuaded and aided by Nazi Germany, took control of Transnistria for the first time in history. In August 1941, Adolf Hitler persuaded Ion Antonescu to take control of the territory as a substitute for Northern Transylvania, occupied by Miklós Horthy's Hungary following the Second Vienna Award(citation need). Despite the Romanian administration, the Romanian state did not formally incorporate Transnistria into its administrative framework; the Nazi-friendly Antonescu government hoped to annex the territory eventually, but developments on the Eastern Front precluded it.
Read more about Transnistria Governorate: Romanian Conquest of Transnistria, Status With Respect To Romania Proper, Administrative Divisions, Population, Organization, The Holocaust in Transnistria Under Romanian Occupation, End of Transnistria Governorate