Arguably, we gave up on stabilizing Iraq and pulled out too quickly, angering the Sunni tribes who were counting on the U.S. to protect them from the majority Shi'ite government. Once they saw the U.S. military bailing out, they began allying with Sunni extremists and gave ISIS a fertile soil in which to take root.
>>bliste+(OP)
US has been mostly used as a very expensive bludgeon to deal with internal enemies.
You don't like your local police officer, call him terrorist and see the world's most expensive bludgeon deal with him. Don't want to deal with rebellious village? Tell Americans they are terrorists.