Pakistanis check the site of a bomb blast in Karachi on Sunday. Pakistani officials say the blast has killed dozens of people in a neighborhood dominated by Shiites. Fareed Khan/AP hide caption

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A fresco painting from the Chehel Sotun Pavillion in Isfahan, Iran, depicts Persian warfare during the Safavid dynasty period. Dave Bartruff/Corbis hide caption

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The Origins Of The Shiite-Sunni Split
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