From memory Andrew Exum was once a familiar name here on the Forum, he moved from being a US Ranger Captain to being a DoD Deputy Asst. Sec. and not a contributing editor for The Atlantic.

This article is his reflections when you ask:
Fifteen years after the U.S. invasion, thereís no satisfying answer to the question: What were we doing in Iraq anyway?
Teese two passages are near the end:
Some 4,500 U.S. troops died in Iraq, and countless more returned home with physical and psychological wounds theyóand we, as a societyówill deal with for the rest of their lives. As a nation, we have sunk more than a trillion dollars into Iraq so faróa trillion dollars you see missing every day in unpaved roads, underpaid teachers, and the social services our congressional leadership tells us we donít have the resources to fund.And are Iraqis even better off? Are they at least an appreciative ally of the United States in the region? Conservative estimates of Iraqis killed in the war tally north of 100,000 dead. The Iraqi people suffered immensely during our invasion and the civil war that followedóa civil war we proved unable to end or even shape. Today, Iraqís political class understands that it needs continued U.S. diplomatic and military support, but Iraqís people largely hate our country for what we ourselves did and for what we then allowed to happen. I canít blame them.