They are Americans, and they are mujahideen. Hundreds of men from every imaginable background have walked away from the traditional American dream to volunteer for battle in the name of Islam. Some have taken part in foreign wars that aligned with U.S. interests, while others have carried out violence against Westerners abroad, fought against the U.S. military, and even plotted terrorist attacks on American soil. This story plays out over decades and continents: from the Americans who took part in the siege of Mecca in 1979 through conflicts in Lebanon, Afghanistan, and Bosnia, and continuing...