Saddam Hussein was dreadful, but Nuri Kamal al-Maliki has been a catastrophe. His virtual elimination of Sunni Muslims from the Iraqi government, beginning with his targeting the now exiled Sunni vice president Tariq al-Hashemi immediately following the withdrawal of U.S. forces in 2011, left Sunni Iraqis with no political power and no way to address grievances. Add to that his increasing authoritarianism, and civil war looked inevitable. ISIS is merely the precipitating factor.
Those currently insisting that Obama "should have" left some American troops in Iraq conveniently forget that Maliki refused to sign the status of forces agreement that would have permitted that. It was clear at the time that Maliki wanted the United States out of Iraq, so he could more easily pursue his sectarian goals.
Now Maliki wants Obama to send air power to help him fight off the ISIS rebels, but without dependable American spotters on the ground, air strikes are more likely to kill hapless civilians than rebel fighters. Old Baathists are joining up with the ISIS forces, Shi'a militias are forming, and QUDS guardsmen from Iran already may be in Baghdad. Quite frankly, any American involvement at this point seems absurd.
I'm waiting for the Kurds to spread out from their autonomous region, perhaps even into Syria, and declare an independent Kurdistan. Their pesh murga is the best fighting force in the region, and the ongoing chaos in Iraq may be their best chance to have the homeland that has been their goal for many years.