Anbar Province holds painful historical import for the United States as the place where nearly 1,300 soldiers and marines died after the American invasion of 2003. Since the beginning of 2014, months before the fall of Mosul and the start of the American air campaign against Islamic State, the United States has been working with the Iraqi government to push back the extremist group in Anbar, sending vast supplies of weapons and ammunition and, more recently, training Sunni tribal fighters at an airbase in the province.