They are the remains of administrative borders during colonial times. They were not meant to create countries, but colonies that could be governed easily (so gerrymandering for incompatible ethnic groups to be bundled together). read more
The borders were largely made during the conference of Berlin and were made by Europeans for ease of resource extraction. Which typically meant dividing up single ethnic group states over multiples countries to keep them from uniting and to keep them as dysfunctional as possible. Thus the borders have no real practical meaning to the people. read more