Of paramount importance is that Americans never again pointlessly fight and die in a region incapable of self-governance, where the American sacrifice of blood and treasure will purchase neither peace nor stability, and where that sacrifice is met with contempt and disregard on the part of the people for whom that sacrifice was made.
Syria and Iraq are not France in 1944, ISIS is not the Nazis; if ISIS is stopped another similar militant Sunni insurgency will reconstitute once the Americans leave, which means we will be forever returning to Iraq to prop up an untenable and failed 'state,' or we will forever remain in Iraq with Americans pointlessly fighting and dying.
The American Century has been over for decades, it's time we realize that.