Know thine enemy

I grew up hearing about the infamous "Hatfield-McCoy" feud. It's absolutely legendary and has become the stuff of legends and myth:

The Hatfield-McCoy feud (1878–1891) is an account of American lore that has become a metaphor for bitterly feuding rival parties in general. It has been described as an Appalachian Capulet-Montague rivalry [[1]] involving two warring families of the West Virginia-Kentucky backcountry along the Tug Fork River, off the Big Sandy River. However, unlike the fictional Romeo and Juliet, the Hatfields and McCoys were violently real.

Wikipedia

And so it goes in the middle east--"violently real":

The critical struggle between Shia and Sunni for the future of the Middle East.

To most Western eyes, all Islamic movements look alike, and the central conflict in the Middle East is one between religion and secularism. Shockingly little has been written about the bitter divide between Shia and Sunni. Yet without understanding their ancient conflict—and its modern embodiment in the power struggle between Iran and Saudi Arabia for political and spiritual leadership of the Muslim world—it is impossible to comprehend events across the so-called Shia Crescent, from East Africa through Iraq and Pakistan to India.

The provocative rise of the Ayatollah Khomeini, the Saudi pressure on the United States not to unseat Saddam Hussein in 1991, the critical role of the Ayatollah Sistani and the religious establishment in Najaf (Iraq), the volatility of Pakistan today, and the consequences of the shift toward Shia power through American intervention—all this and more is explained in the light of the Shia/Sunni divide.