Iraq was beaten thoroughly, in the sense that the central government and its army was destroyed. The population in Iraq had a more ambiguous relationship to the central government than either Japan or Germany. There is no cultural unity underlying Iraq as there was in Japan and Germany.
I'm not sure that Vietnam is a good comparison. I don't think there was much doubt that once the US left Vietnam, there would be a unified country. It would be a nationalist and communist government, but it would eventually control the country which had a long cultural history (I think)

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13