Brigadier Hidayat Abdulkarim, the former head of Iraq’s Third Brigade, by extension the defense of Mosul, says that internal ethnic and sectarian divisions in the military were the primary reason for the city’s fall.
Abdulkarim, a Kurd, says he didn’t even learn about the fall of the city until the following morning, and that despite being nominally the brigade leader, he was effectively only in control of about one and a half regiments, with the Shi’ite majority largely ignoring orders.
Abdulkarim reported Sunni Arab troops deserted over a week before ISIS arrived, apparently tipped off to the fight, and that the Maliki government undermined his command by refusing to give his unit equipment.
How much of this is real and how much is after-the-fact excuses is unclear, though it seems plausible given the sectarian and ethnic tensions in Iraq. Abdulkarim says he was only given the promotion because of backing by President Talabani, and since being sought for court-martial has been living in Kurdistan.