It seems to me that Bush needed backing to legally go into Afghanistan. I believe he needed a UN resolution, and I seem to remember that NATO had a role in the UN resolution. I'm a little hazy on that. Didn't Norway send about 20 troops? Then, our generals sent the Afghan army to catch Osama in Tora Bora (now apparently occupied by ISIL) and that didn't work out. After that, at the time, I could see no further reason for our presence in that country. Maybe our allies pulled out in disgust?