Situation you describe is not unique for former colonies all around the world, how breakup of former empires was generally handled is the peak of colonial incompetence and worse, and most of Africa and Middle east are a huge mess due to that.
Its one thing when one draws a nice square around Wyoming for example, another when such straight line makes you suddenly part of country led by your rival tribe, with different religion, priorities and often outright hate towards you (and usually long history of violent conflicts to build upon).