The war blew away that gentility, those ideals and that faith in progress. Ernest Hemingway captured the rising irony and cynicism in “A Farewell to Arms.” His hero is embarrassed “by the words sacred, glorious and sacrifice and the expression, in vain.” He had seen nothing sacred in the war, nothing glorious, just meaningless slaughter.

European culture suffered a massive disillusion during the conflict — no God, no beauty, no coherence, no meaning, just the cruel ironic joke of life. Cynicism breeds a kind of nihilism, a disbelief in all values, an assumption that others’ motives are bad. It makes it hard to see the good that remains.

Fussell wrote that the war spread an adversarial mentality. The men in the trenches were obsessed with the enemy — those anonymous creatures across no man’s land who rained down death. “Prolonged trench warfare, whether enacted or remembered, fosters paranoid melodrama,” he wrote.

The “versus habit” construes reality as us versus them — a mentality that spread through British society. It was the officers versus the men, and, when they got home, the students at university versus the dons. “Simple antithesis everywhere” is how Fussell captured the mentality. Along with it was what T.S. Eliot called a “dissociation of sensibility,” in which thoughts of tenderness and care are cut off from reason and calculation.

George Orwell wrote that he recognized the Great War mentality lingering even in the 1930s in his own left-wing circles — the same desire to sniff out those who departed from party orthodoxy, the same retelling of mostly false atrocity stories, the same war hysteria. As Christopher Isherwood put it, all the young people who were ashamed of never having fought in the war brought warlike simplicities to political life.

Some of the disillusioned drop out of public life, since it’s all meaningless. But others want to burn it all down because it’s all rotten. Moderation is taken for cowardice. Aggression is regarded as courage. No conciliatory word is permitted when a fighting word will do.

Today we face no horrors equal to the Great War, but there is the same loss of faith in progress, the reality of endless political trench warfare, the paranoid melodrama, the specter that we are all being dehumanized amid the fight.