On looking into a selection of Sassoon's verse

The first half—up to and including 1915—is all starlight
and roses and misty dreams; like he wrote these poems
with a daffodil wilting in his hand, yearning vaguely
towards the horizon. This is the work of an effete young
man with too much money and time on his hands. It's
watery stuff that runs through the mind and leaves no
mark. Bapaume and Carnoy are yet to come.

The second half—mud; then blood; then mud and blood
and spattered brains and God knows what else. Reality
has risen up and kicked this man in the guts. There in
the trenches, among the sodden mangled dead, Sassoon
is shocked into writing what's in front of him, not what's
far away and over the moon. And, through him, we see
what it all came to—the posturings of Empire, the pomp
and strut of statesmanship, the glittering brilliance of the
Viennese court, the old men's political games—all that
came down to stinking boots and rotting corpses and the
intestines of the man next to you spilling into your lap.
In Sassoon's verse the long 19th century quivers and
dies, and the 20th century arrives like a grinning skull,
accompanied by a scamper of rats.