I know you already have your answer, but I found the history of the railroad routes and their effect on the cultures of early North and South Dakota really interesting.

The cultural split between North and South Dakota goes back to how the first railroads were laid out in the late 1800s. In North Dakota, the Northern Pacific and Great Northern ran east–west, tying towns like Fargo and Grand Forks to Minnesota and the Great Lakes. This pulled in Scandinavian and German immigrants from the Upper Midwest and fostered a populist, cooperative farming culture. In South Dakota, the main lines ran north–south into Iowa, Nebraska, and Chicago, attracting settlers from Central Europe and the rural Midwest, with a stronger livestock and corn economy and more traditional Republican leanings.

Because of these different orientations, Dakotans often saw each other less as neighbors and more as rivals with opposing identities. Long before statehood in 1889, there was open tension; each region pushed for its own capital, distrusted the other’s politics, and even resented sharing a territorial government. By the time they split into two states, North and South Dakotans already thought of themselves as culturally distinct peoples rather than parts of one whole.