Doesn't really make sense if it's Islamic guys shooting their own brothers.
Shi'i and Sunnis kill each other over who Muhammad left in charge of the caliphate (an Islamic state led by a caliph, who is a political and religious leader and a successor (caliph) to Muhammad. His power and authority is absolute.)
Shias believe that Ali and the other Shia Imams are the rightful successors to Muhammad. This disagreement split the Ummah (Muslim community) into the Sunni and Shi'i branches.
Ali was Muhammad's son in law - nepotism at its finest (the practice among those with power or influence of favoring relatives or friends, especially by giving them jobs)
Muhammad Ali (the boxer) must of been Shia
Yes, I am looking stuff up. My main source is Wikipedia.
'Allahu akbar!"