so I'm in the process of creating the map of my fantasy world, which has a medieval fantasy theme. I saw a few posts and videos, such as this one, that talk about using Natural Borders to define my borders: https://www.youtube.com/watch?v=iZJJpy3huLg&t=618s
Right now I'm adding my mountains before I start adding my rivers. However, I do not want to have mountains that go all the way to the coastlines, like it's on this video, and block regions in strict ways to create my nations. Throughout history, I do want my nations to have wars and have road connections for trade, and be able to travel from one another. And I'm presenting them as kingdoms, not nations.
If I have a situation like this image here:
where the mountains separate two areas, but still allows a comfortable area on one side for people and armies to pass, does it still make sense to have these two regions as two separate kingdoms, with two different cultures? Or does it have to be one big kingdom, simply because the mountains do not completely separate the two and over history, it will make more sense to be unified?
I understand that rivers, resources, and history/politics will also determine what makes a kingdom, but I just want to get your advice from this stage before I make much progress and avoid the need to go back and re-edit the map.