system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 why is the German state of north Rhine westphalia so largely populated? are there any agricultural or climate factors as to why it's as populated as it is,?
gpt
Several reasons actually.

1. From 12 thousand coal miners in the mid 19th century, the region grew to 400 thousand coal miners in the early 20th century. It's a lot easier to build factory right next to where the coal is, so that's where a lot of cities that grew in size as industry grew, jobs were created and this attracted people from the rural area. Coal in that area was also very close to the surface, making it a lot easier to find and to exploit.
2. Rivers always played a big role in trading and this region have a lot of them, especially two big ones. The industrial region is called the Rhine-Ruhr for a reason, as those two rivers cross right in the middle of a dozen of big towns and cities. The Rhine especially is one of the biggest river for commerce in the region and finish in the Netherland where you can find the biggest trading port of Europe, Rotterdam. The rivers and coal are also the reason why the low countries are so densely populated.
3. The Sauerland and the Bergisches land are two hilly region just South-East of the the State. There is Iron mines there, but of low quality. That said, the hilly nature of the geography meant that these region had a lot of rivers with high water power. These made them very useful for some industries like metallurgy and textiles.
4. A bit more south of the Sauerland is the Siegerland, which is at the border of the State. This is a more mountainous region and here you can find a lot of high quality iron mines. So the iron was mined there, then it was transported along the rivers to the Sauerland and Bergisches land region for processing, then transported again via the rivers to the Rhine-Ruhr region where all the industry could use the iron.

The region had some decent agricultural land, but this isn't the reason why it's more densely population. Region with a lot of Arable land tend to be less populated. North-Rhine Westphalia is the German State that import the most food.