Because of the bull headedness of the President George W Bush administration, the Iraqi Army of the Saddam Hussein era was disbanded after the US invasion of Iraq. Water over the dam except for it’s recurring costs to the Iraqi and American people…
So we reconstituted the Iraqi Army and armed and trained them and they collapsed under the assault from ISIS.
So now what are we doing? Well we are reconstituting and training Iraqi troops to repel ISIS and retake captured territory. Whey would we expect this to work the second time?
You want to build a wall around something? I suggest the middle east and let the neighbors sort it out.