WWI is often credited as having led to the disillusionment that gave rise to post-modernism. Is there evidence that WWI soldiers themselves experienced personal disillusionment?

English/history Major here, and infrequent poster so any clarification that can be lended is appreciated.

The assertion that post-modernism stems from WW1 is a bit of an oversight. WW1 was instrumental in the cultural shift into modernism, which of course led into post-modernism, which of course share many similarities but have subtle, important differences.

But, a great question regardless, and the aspect of the soldiers anguish of the great war is a fantastic aspect of literary development of the time. Poets such as Wilfred Owen, Siegfried Sassoon, Isaac Rosenberg and so on, were poets who were soldiers on the front lines and wrote uncharacteristically grotesque depictions of war. War poetry prior to WW1 was a glorification of the classical (stemming from The Iliad especially), and the mythical in war. An example of this is The Charge of the Light Brigade by Tennyson, which depicts the 'heroic' and 'tragic' suicide run of cavalry into a barrage of artillery. the difference in language used shows the clear diversion from myth building into trauma induced terror:

"Cannon to right of them,

Cannon to left of them,

Cannon behind them

Volley'd and thunder'd;

Storm'd at with shot and shell,

While horse and hero fell,

They that had fought so well

Came thro' the jaws of Death

Back from the mouth of Hell,

All that was left of them,

Left of six hundred."

Compared to:

"If in some smothering dreams you too could pace

Behind the wagon that we flung him in,

And watch the white eyes writhing in his face,

His hanging face, like a devil's sick of sin;

If you could hear, at every jolt, the blood

Come gargling from the froth-corrupted lungs,

Obscene as cancer, bitter as the cud

Of vile, incurable sores on innocent tongues,--

My friend, you would not tell with such high zest

To children ardent for some desperate glory,

The old Lie: Dulce et decorum est

Pro patria mori."

The namesake of the Poem, Dulce et decorum est, pro patria mori is latin for "it is sweet and right to die for ones country". Owens here, after describing a horrific experience with a gas attack, declares it an 'old lie'. The evidence of this all being soldiers disillusionment is that many of these poems were written in the trenches. Owens himself did not survive the war.

While that is a lot about poetry, it extends to other literature also, especially novels. Such examples are All Quiet on the Western Front, A Farewell to Arms and Good-Bye to All That, by Erich Maria Remarque, Ernest Hemingway and Robert Graves respectively.

Furthermore, elements of 'modernist' skepticism was present prior to WW1. This can be seen strongly in Joseph Conrads Heart of Darkness, (Apocalypse Now is a modern adaption of this) wherein a similar vein of anti-colonialism and criticism is present, but in relation to the Congo under Leopold.

Hope that helps, and like i said if anyone can help with further input or corrections it is greatly appreciated.

Sources:

Bennett, Andrew, and Nicholas Royle. An introduction to literature, criticism and theory. Harlow, U.K. New York: Pearson/Longman, 2009.

Conrad, Joseph, and Paul B. Armstrong. Heart of darkness : authoritative text, backgrounds and contexts, criticism. New York: W.W. Norton & Co, 2006.

Walter, George. The Penguin book of First World War poetry. Melbourne, Vic: Penguin Group (Australia, 2014.

Edit: Formatting, corrections.