When the distances are greater they're more likely to just declare a particular longitude / latitude to be the border. And nobody's quibbling over who owns a particular patch of the desert, at least until they find oil or something out there.
Also, improvements in transportation tech did in fact change the scale of how things are managed.
There's actually a really neat bit of research that was done way back (G. Edward Stephan), looking at county size evolution. Basically, when it was horseback, as population expanded, new centers of administration would spread with them, maintaining a specific (logarithmic) ratio of density vs size, and borders would fluctuate over time. But after railroad and later the automobile were invented, the pre-existing borders at that point in time basically stopped evolving, leaving a lot of long straight lines on the map, whereas prior to that, they would have evolved based on transport efficiency.
http://www.uvm.edu/~pdodds/files/papers/others/1984/stephan1984a.pdfSo, many of the pre-existing small counties in the East are basically too small for full efficiency, given modern transportation tech, but there's political inertia keeping the borders where they are.
It turns out those old counties have a very strong mathematical relationship. They're at the optimal size vs density to minimize the travel time (assuming horseback) for a central administration to service any particular person who lived at that time. This same mathematical equation also seems to predict the size of whole nations and empires throughout history. This suggests that logistical efficiency plays a part in where borders were, historically, and not just politics.