It is characteristic of those intellectuals and officers who wrote about the Great War of 1914-18, that they experienced a permanent disillusion leading to the attitude epitomized by Robert Graves's autobiography "Goodbye to all that".
In other words, the typical effect of the Great War was some combination of a rejection of tradition generally but especially Christianity; the embrace of hedonism - especially sexual, but also drinking and smoking, jazz etc.; socio-political leftisms of various types - communism/ socialism, fascism, pacifism, vegetarianism, 'green' ideas etc; an intense, tragic and paralyzing, yet guilty, nostalgia for the care-free privilege and security of the Edwardian era; and all underpinned by a bleak combination of philosophical materialism and hopeless nihilism.
But, as John Garth makes clear in Tolkien and the Great War, this did not apply to Tolkien. He was deeply affected by the war, his trench experiences, and especially the deaths of so many friends (i.e. all but one of his closest friends) - yet Tolkien was not permanently embittered nor disillusioned by the War, nor was he impelled to adopt the above-listed 'typical' literary responses.
What made Tolkien immune to this existential aspect of the war? I think the answer is quite simple; and it is that Tolkien had a deep and powerful Christian faith.
In contrast, from what I can tell, those who experienced the disillusion of the Great War either practiced a shallow and merely conventional Christianity, that rapidly and permanently collapsed under the intense and sustained psychological and physical pressures of trench warfare...
Or else they were not Christians at all, and the war confirmed their pre-existent conviction that the reality of life was nasty, brutish and short - and the only valid response was to live for today oneself, and agitate for a more peaceful, prosperous and secure society in future.
Many of the most disillusioned men were intensely artistic and aesthetic people, intensely political and reformist in outlook, and 'romantically' dedicated to a life of intense personal relationships. But they failed to learn from the fact that none of these - nor all together - were able to cope with the stresses and sufferings of the Great War.
Instead of noticing this failure of their ideals - instead of noticing that their own disillusion proved that their ideals were illusions - they doubled-down on their ineffective strategies... And have continued to do so in the many decades since.
The failure of secular ideals taught the failure of trying to live without religion.
And something analogous applied to mainstream Victorian/ Edwardian Establishment Christianity: it had been tested, and it had failed the test.
The failure of mainstream Christianity taught the failure of the churches.
Things could have been otherwise...
Tolkien, as so often, showed the proper and effective way forward - because he was both a Romantic and a Christian.
I think the same applies to this era.
The mainstream churches have been taught that they have failed in the face of crisis; the leftists have been taught that their ideals are incoherent and based on lies, propaganda and coercion.
We know what has failed - now we need to seek what is both good and strong.