The rapid progress made by Sunni rebels has focused attention on the performance of the Iraqi national army - which has in some places melted away without putting up a fight.
Some trace the army's problems back to the US-led invasion of Iraq in 2003.
Paul Bremer was the senior US diplomat in the country at the beginning of the US occupation. He says the current crisis in Iraq is the fault of the current political leadership.
Al Jazeera's Fergus Nicoll reports.