Germany and Japan also consisted, mostly, of a single ethnic group.
Contrast that with Iraq, which is a shotgun marriage of three hostile, incompatible groups - hardly the same.
Post WWII, Japan also enthusiastically adopted Western culture, values, even our legal system. Again, can you say the same about Iraq?
I think they will eventually, not without problems. But I think there's been more progress in that area than the media has led on.