"Unlike the Americans, whose occupying forces were largely disciplined, the French troops, especially it seems a minority of the feared colonial troops from North Africa, looted extensively and perpetrated numerous rapes on entering German villages and townships....In Freudenstadt, the worst instance, the raping, looting and pillaging went on for three days" (Ian Kershaw, The End. Hitler's Germany 1944 - 45)
I didn't know that until I read Kershaw's interesting new book. I just assumed that only the Russians had done such things - they did do them, simply on a larger scale.
It may have been different in 1945, as Kershaw asserts, but we have known for decades that American Army discipline isn't very good. Discipline isn't just about getting men to Charge! when they are told to Charge! but also about them doing the job they are sent in to do and only that job. Letting off frustration, lording it over locals, indulging personal viciousness are not usually part of the job.
Discipline is also about withdrawing from combat duties soldiers who appear disturbed to their comrades, who bully or boast or hate too much.
It's clear that American soldiers in Afghanistan, just as in Vietnam and Iraq, are not adequately disciplined. Nor are British soldiers. The result is that instead of defeating enemies, the Americans and the British have made new ones. If that's the best you can do, then you shouldn't deploy your "Heroes" in the first place.