A Map of Shadows

[Karro]

Tripoli and Cyrenacia, as well as most of the north african states, have extremely weird borders. Borders of states/countries are usually either in straight lines or jagged edges, very rarely along a curve.

I don't think those are meant to be hard borders, really. South of those borders is land occupied by various "desert tribes". I think when your land borders a nomadic, ill-defined, or porous peoples, then your "borders" with them are going to be nomadic and porous - basically the border is where your defensible settlements end or where the extent of your authority and influence drops below a certain threshold.

Basically, I think you're right that borders between sovereign nations with governments that can reach the entirety of their claimed lands tend to be along straight lines or follow "jagged" natural boundaries, but I don't think "desert tribes" counts as a sovereign nation in the traditional sense.