If we couple together the entire Indochina fiasco (not just Vietnam but also the bombing of Laos and Cambodia) I'd say it's a probably a clear choice. The loss of life just from bombing campaigns alone is absolutely astonishing. After that I would probably say Iraq/Afghnistan (The War On Terror), if only I knew enough about it to have made up my mind on it. I hear persuasive arguments from both sides and to this day, after many years of looking at it (from my armchair) I cannot come to a definitive conclusion. I also hear pathetic arguments from both sides that I find contemptible and make me want to hop the fence. Things like the constant crying about the lies regarding WMD's, from the anti-war movement, as if the Bush administration lying invalidates a particular cause. Or that because we used to support Saddam and Al Qaeda that we therefore forfeit the right to reverse the policy towards them. Again... Or take the pro-war side, saying things like we can't allow what happened on 9/11 to go unchecked. Oh really? Then I suppose you're also in favour of systematic bombing and a land invasion of North America for the US's terrorist atrocities which far outweigh bin Laden's and Al Qaeda's, not to mention the support of their hosts. Beyond that it'd be a toss up between authorising genocide in East Timor, and the support for ethnic cleansing in Turkey throughout the 90's. What would you say?