In 1937, it lost the exclave districts of Eutin near the Baltic coast and Birkenfeld in southwestern Germany to Prussia and gained the City of Wilhelmshaven; however, this was a formality, as the Hitler regime had de facto abolished the federal states in 1934.
By the beginning of World War II in 1939, as a result of these territorial changes, Oldenburg had an area of 5,375 km2 (2,075 sq mi) and 580,000 inhabitants.