I read that hundreds of thousands of young male aristocrats, many who were officers, who would have been the next generation of governing leaders, died in WWI along with millions of 'ordinary' people, which I guess hastened the end of leftover centuries-old medieval-class relationships which probably had given comfort, continuity and stability to most European people of the early 20th century. But Leadership didn't die, just the generation educated to rule by maintaining class divisions beneficial to that upper class died.
Adding to the psychological turmoil, in surviving ongoing warfare it means you get sent to the front on multiple tours, but I think wars before WWI used to have long pauses in the conduct of war, which was no longer possible in WWI due to the advances of war mechanization. In addition, the aftermath of every war fought that is close to home is a huge upheaval because of the resulting shortage of young men, big disease vectors, transfers of and new concentrations of wealth, and disrupted markets.
But added to the usual wartime disruptions, I think, WWI was the first war which had massive long-distance killing, not the more honorable warrior to warrior battle. Thinking about fighting sword to sword probably feels different emotionally than thinking about being killed by invisible shrapnel or powerful percussions that come out of nowhere without pause from hours of constant shelling, or gas which suffocates you invisibly. I can only imagine it. I've heard accounts from Vietnam fighters, and I guess among the usual horrors that cause PTSD nerves, in particular, was not being able to see anything because of the thick jungles combined with the distances bullets could travel invisibly. I think the change from single face to face combat to sudden mass mechanized weapon death on an army unprepared by training or TV or movies or video games (I'm not being flippant) was exponentially devastating. I know everything about war is bad, but I'm guessing if you can't see, hear, or feel the distant man that is killing your friends who are sitting 1 inch from you despite your weapon it's a more searing experience, even with mental preparation.
Among the few rewards of being a warrior is that mano y mano victory - I believe it's biology-based for men. When a person's strength and intelligence and value is made moot simply because where you accidentally happen to be standing or sitting shrapnel strikes, it probably feels unjust, wrong, unfair, whimsical, more pointless, more meaningless, and random than you can prepare for. I think unquestioned patriotism and honor would be harder to hang on to, and you'd think more deeply about everything you believed about the protective 'shields' of religion, societal mores and expectations, being a good person as a strategy for deserving to stay alive, having purity of purpose to make certain of winning, getting an education to make you too smart or valuable to be killed, etc.
For most Americans, the closest experience of the personal possibility of death comes from car or sport accidents and illnesses. Many people, of course, rely on the normal life patterns surrounding them for reassurance that they were magically protected from death. In war, though, there are no normal life patterns around them; soldiers become aware that anyone can die and no one has magical immunity. No prayer, no amulet, no ritual, no strength or skill, no powerful person or strategy, nothing can protect you from a sudden act of warfare in the miles of physical space around you. In the days of battle you see perfectly decent, good, family men chopped mercilessly into pieces despite their utilizing every bit of training and good fortune.
Eliot, I think, a literary man who had faith in literary wisdom and social norms, discovered how small of a protection lessons of wisdom and defined norms were against the desire for massive wartime deaths and maiming, and in a personal tragedy a very damaging marriage which was difficult. In that moment in time, that decade, he raged at the ultimate impotence and lack of protections that the ideas in classic literature, which in his earlier youth and inexperience had sustained him, along with social norms, actually had in reality to impact human civilization. He wasn't simply showing off his erudition, I think he was probably ranting at literature, society, religion and culture for failing to stop the 'collapse' of said same. The poem is full of allusions to those myths and wiseman sayings which reflect the darkness in humanity rather than the wisdom. He includes bits of memory which emphasize the cluelessness and obtuseness people have of their personal lives. In my opinion, most Westerners suffer at a certain point in their lives through this perceived 'collapse of civilization' at some point in their lives because they think society has moved away from the classic ideals which maintained the life they imagine they grew up in, but in most cases, civilization continues on in its true identity and it's the veils of classic idealism that the observer was looking through that were ripped way. To a child, the world is a description. Grown ups do their best to live ideally, but I think true wisdom is accepting that the best we aspire to we often fall short of, but we need to get on anyway. This poem obviously does not have this viewpoint since its a rant of despair.