I am not sure which forum to put this in, so I will put it here. Do you think that drainage divides, the lines that separate two different river basins from one another, serve as good national and state borders? The US states of Montana and Idaho have some of their borders defined as drainage divides. In a timeline I am working on, the US annexes more of Mexico, but I have heard that the US wouldn't follow Mexico's already established state borders, so I was wondering if it would be a good idea to use drainage basins. Keep in mind, they are ideal for managing water resource and are usually defined by mountains, so the US-Mexico border would be a mountain range.