What is the difference between a shiite and a sunni and a kurd?

These 3 groups are playing an important role in the new governemnt in Iraq, but I don't understand how they can be that different, since they are all muslims. What is the difference and why? In america, there are different christian groups, but I don't see them divide into political parties like in Iraq. ... show more These 3 groups are playing an important role in the new governemnt in Iraq, but I don't understand how they can be that different, since they are all muslims. What is the difference and why? In america, there are different christian groups, but I don't see them divide into political parties like in Iraq. Are there such big differences that cause this?
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