Because the Ruhr region was an area of high residential density and a centre for the manufacture of weapons, it was a major target in the war.
Women with young children, school children and the homeless fled or were evacuated to safer areas, leaving cities largely deserted to the arms industry, coal mines and steel plants and those unable to leave.
The first Jews from Bochum were deported to Nazi concentration camps and many Jewish institutions and homes were destroyed. In December 1938, the Jewish elementary school teacher Else Hirsch began organising groups of children and adolescents to be sent to the Netherlands and England, sending ten groups in all.
Some 500 Jewish citizens are known by name to have been killed in the Holocaust, including 19 who were younger than 16 years old. Many Jewish children and those from other persecuted groups were taken in by Dutch families and thereby saved from abduction or deportation and death.
The urban area is divided into the river Ruhr catchment in the south and the Emscher catchment in the north.
The Ruhr's tributaries are the Oelbach (where as well a waste water treatment plant is established), Gerther Mühlenbach, Harpener Bach, Langendreer Bach, Lottenbach, Hörsterholzer Bach and the Knöselbach.
The Opel Astra is assembled at the Opel Bochum plant; however, by 2009, the factory was in serious financial difficulties In the course of a comprehensive community reform in 1975, Wattenscheid, a formerly independent city, was integrated into the city of Bochum. In 2007, the new synagogue of the Jewish community of Bochum, Herne und Hattingen was opened.
Bochum acquired city status, incorporating neighbouring towns and villages.
Additional population gains came from immigration, primarily from Poland.
In 1321, Count Engelbert II von der Marck granted Bochum a town charter, but the town remained insignificant until the 19th century, when the coal mining and steel industries emerged in the Ruhr area, leading to the growth of the entire region.
The population of Bochum increased from about 4,500 in 1850 to 100,000 in 1904.