Complex sentence: Its town hall Rathaus Schöneberg was completed in 1914 and served as the city hall of West Berlin until 1991 when the administration of the reunited City of Berlin moved back to the Rotes Rathaus in Mitte.
Split into simpler sentences: Its town hall Rathaus Schöneberg was completed in 1914. Subsequent to World War II it served as the city hall of West Berlin until 1991 when the administration of the reunited City of Berlin moved back to the Rotes Rathaus in Mitte.