There's nothing on the fantasy map makers that lets you designate areas as controlled by one country?
Terraria Community Forums
Tibithia Σ
Streyll
Well, so far the best fantasy one I've found is Inkarnate, but at least the free version has nothing for that.
Streyll
I've seen that one as well, but the problem is I need something I have a bit more control over, as I don't need a generator, I need something I can use to draw borders with and update them over time. And so far it seems I may not be able to do that with that one.