Further to the previous post:  Part of the cost:  "..they [the Iraqi military]  all but collapsed this spring in the face of the advancing militants of the Islamic State, despite roughly $25 billion worth of American training and equipment over the past 10 years and far more from the Iraqi treasury. "  (from the New York Times, Nov 23, 2014).  -----  Part of the answer to "how could this happen?":   A number of new articles explain the failures of the Iraqi military as partly due to corruption in the leadership by the Iraqi military officers, and due to local populations in some areas of the country who support the Sunni Muslim Islamic State in preference to the mostly Shia Muslim based central government.