Before World War 1, there was a (relative) period of some peace, and something insane happened - people started glorifying war. The idea of war bringing out the "real" in a person, or skimming off the excess of society was a thing.

Then of course, once mustard gas is rolling through your neighborhood, glorifying war seems rather stupid.

People are dumb forgetful creatures, but it's important to keep well in mind that war is terrible and horrible, and we as people never want it. Public opinion won't prevent another war from happening ever, but it will make war much harder to argue for.