Answer:
The abundance amount of coal mines.
Step-by-step explanation:
The Ruhr valley became Germany's first industrial center because of the availability of the coal that helped in emerging steel and coal industries. Many of the cities in the Ruhr region came up with a lot of heavy industry. The industrial areas of the Ruhr came under the district of North Rhine-Westphalia, which included places like Bergische. The cities and urban districts of the region grew independently during the Industrial Revolution.