"We have done fairly well in winning the battle, we have not always done well in winning the wars, because we have not had the things in place to rebuild and create conditions for success after the fighting has ended," Stewart stated.
Stewart was asked about the pending operations to retake the Iraqi city of Mosul from Daesh control, and preparations for the aftermath of that fight.
"We are now starting to isolate Mosul. I would imagine that operation will unfold sometime in the next two to three months," Stewart noted.
Earlier on Thursday, commander of the US-led anti-Daesh coalition Lt. Gen. Stephen Townsend estimated that the operations to re-take Mosul could begin as soon as the next few weeks, led by Iraqi Security Forces and Kurdish Peshmerga, who have been trained and equipped by US special operators.
The United States has been working with Iraq to try to restore security and improve governance after the US invasion of the country in 2003.
President Barack Obama acknowledged that failing to effectively prepare for the aftermath of the US-led invasion of Libya was the worst mistake of his presidency.