By Aryn Baker | Photographs by Lynsey Addario for TIME First they shot her husband. Then the soldiers killed her two sons, ages 5 and 7. When the uniformed men yanked her daughter from her hands next, Mary didn’t think it could get any worse. Mary and her family were members of the Nuer tribe in South Sudan, caught up in a vicious power struggle between the new country’s President Salva Kiir, a me