20 years after the U.S.-led invasion, what has changed in Iraq?

Read MoreU.S. troops left in 2011 but returned as the country was gripped by sectarian bloodshed and the rise of ISIS, and Iraqis struggle to believe the nightmare is over.U.S. troops left in 2011 but returned as the country was gripped by sectarian bloodshed and the rise of ISIS, and Iraqis struggle to believe the nightmare is over.