i think USA overstreched itself, they should've just focus on Afganistan and couple of most dangerous terrorists, instead of going into all out war with anything hostile towards US. If they would effectively dealt with couple of worst problems, they would scare others. As it stands they didn't really solve anything. Iraq and Afganistan are a mess just wating to blow up again and no terrorist organizations have been dismantled. It just gives courage to others to stand up against USA and attack it.
Plus they blew up all the support from international community they had after 9/11.
The biggest concern for the USA right now must be that the war doesn't spread. If it spreads it will sooner rather than later pull in americans, whether they want it or not. I don't think US can handle another war as easily as they do the one in Iraq.