The Iraqi Army that disintegrated under an onslaught by Islamist fighters last week was a hollow force, riven by corruption, poor leadership and sectarian splits — a shadow of the military Washington had hoped to leave in the war-ravaged country.

The United States dismantled Iraqi dictator Saddam Hussein's military after invading in 2003 and spent $20 billion to build up a new 800,000-strong force, banking on its ability to keep the peace when the U.S. military withdrew in 2011.

While the 2003 decision to disband the army led to a bloody civil war, Iraqi forces were seen as generally competent by 2011 and sectarian fighting had eased, giving U.S. President Barack Obama some confidence as he pulled out all American forces.