Encourage The Ruhr Boom is a regular decision for 
Prussia, 
North German Federation, and 
Germany.
Ruhr-area was an agrarian part of Germany until the 1850s. The demand for coal was skyrocketing because of machines getting bigger. The Ruhr-area was targeted by coal miners in response to the high demand for coal, the area experienced industrialization like no other. The population grew in the Ruhr area and its importance also grew as well.
You'll have to research Market Structure, Organized Factories, and Early Railroads to enact the decision. You'll also have to own Dusseldorf, Siegburg, and Cologne to make the decision appear. Prussia owns all three provinces at the start of the game.
Prussia will have 10% more population growth, -50% factory owner cost, and 50% factory throughput. Undeniably this will help your economy a lot, but be aware that more throughput means more input for factories. So be cautious about unsuccessful factories and consider not subsidizing them.
Ingame description
The Ruhr area, formerly parts of the counties of Berg, Mark and Cleves, is changing day by day. Every day new coal pits, mines and shafts are opened up to supply the ever expanding Prussian railway networks, and lately, supported by imports of British industrial technology, factories are springing up like mushrooms after an autumn rain. The Ruhr is booming, and the example could easily spread to the rest of Germany, if only it were given a little nudge out the door.
- In the code it's called "the_ruhr_boom" instead of "encourage_the_ruhr_boom".
- You'll unlock Support The Krupp Family decision by enacting it.