I once had what I thought was a brilliant idea for a historical AU novel where North and South Carolina were East and West Carolina instead. The logic of the split was sound, but the rest of the plot was ridiculous. Still, the geographical idea has stuck with me for a few years.
The politics of the place were such that the states remained in loose alliances under the Articles of Confederation, which blossomed into a full out war between the Carolinas in the early 1800s. You can probably tell that my American history is pretty rusty. After the war, Durham and Columbia were the two places that remained for free trade between the states and political discourse—i.e. the only two places Easterners and Westerners would be free to mingle without fear of violence.
At one point, this all made sense to me, but I’m not entirely sure the logic is all still there. Here’s a pretty map, anyway.