To say that the split between Sunni and Shia is religious not political is not completely correct.
Part of the picture can be illustrated by looking at Ireland, and the angst that was seen in the 26 Irish counties that are Catholic, and the 6 Northern Ireland couties that are Protestant. It's more than what church one goes to...there are many political and social factors to the divide. Example: whether divorce should be legal or whether it should be forbidden under civil law as well as Canon law.
Another part of the picture is how people are categorized. In the US, the government categorizes us by race. In the American society, we also (rightly or wrongly) characterize one another by race. In the Middle East and the Indian Subcontinent...areas where racial diversity is minimal...people are categorized by religion. Within these categorizations are very powerful ethinc, cultural, and sociopolitical ties, and not all are alike. Example: the Kurdish people are Sunni, as are the Baathists.
And hence, the fighting. The news reports these differences as religious, but there is so much more that seperates them.
Thanks for letting me butt in