The change during/after Vietnam is exceedingly easy to explain: The USA lost the war. History has proven time after time that the loser of a war is always wrong and to blame for all the suffering. It doesn't even matter who started it all or for what reasons. No doubt that was bitter medicine for the Americans after all the wars they had won, especially WWII.
Europe has little real power now, after centuries of dominating the world, so it's understandable the former powers here aren't happy with the new powers muscling around instead. Many of the smaller countries of Europe, for their part, have often enough felt what it's like to be mere playthings for the big players, which is plenty of reason to feel unhappy when they see it happening elsewhere, as it reminds them of their own past. And then there's a country like Sweden who has never suffered anything but instead grown only richer selling weapons to the world in flames around it. Who knows why they bother to say anything, but I guess they feel so divine that they feel like everybody could benefit from their untouched wisdom.