I cannot begin to imagine America's response to an occupying force of foreign military members. Why should we impose that on the citizens of other countries? With military technology today, there is nowhere on planet earth we could not be with troops and supplies within 24 hours, and it costs too much to keep troops abroad.
In certain circumstances, it is necessary that troops not be withdrawn. Bringing the majority of troops back from Iraq was a good move, but only after we had set up the country for some semblance of peace and organization. It's never a good idea to go to another country, make a huge mess, and simply walk away. The work must be done, even after the war is "over." That being said, we should also do better at taking care of ourselves before plunging into another war to our own neglect.