I always thought it was related to Industrial Revolution coming to Germany. There was even iron works and locomotive factory in central Berlin during that time

I always thought it was related to Industrial Revolution coming to Germany. There was even iron works and locomotive factory in central Berlin during that time. The area was aptly nicknamed "Feuerland". A bit further north there was an extremely densely populated residential neighbourhood. Factory workers were living there in terrible conditions. One building (5 floors) had over a thousand tenants. Usually there was only one bathroom for the whole floor. And there was no hot water. Crime and pollution was a huge problem. The architecture was great, at least compared to post-war times, but life in the city was quite crap.