I like it, except for the river violations. You've got another one just below the "A" in "SAFINA". Rivers don't cross one another. When they meet, they join. This is one is actually worse than the one near Lorax City, which could plausibly be justified as a canal.

As to the use of "natural borders" that depends on a suitable barrier existing in the right place, which isn't always so. Rivers more often join than separate pre-modern cultures, where water travel is the fastest, as well as most efficient, means of transportation. In many regions, borders were only roughly defined until they reached the era of treaties and there are places in the world where it is still pretty unclear on the ground where the border lies. That said, these nations are noticeably "boxy".