BAGHDAD, Iraq - For months, the young Shiite couple could not decide whether to move from Dora, a mostly Sunni Arab neighborhood and one of Baghdad's most dangerous. After death threats, the murder of a neighbor and the birth of their first child, they decided it was time to go. High rents kept Rana Ali and her husband, Hussein Youssef, from finding a new home in one of the capital's safest areas, where Shiites are dominant, and they could not afford refuge in Iraq's overwhelmingly Shiite south. Instead, they settled in nearby Saydiyah, another majority Sunni area only marginally safer...