Siegfried Sassoon and Wilfred Owen are English poets and soldiers who both served during the First World War. Many of their poems deal with various themes about the war, including the repercussions of it. As such, they are often referred to as part of the Great War poets. As Wilfred Owen writes in the preface to The Poems of Wilfred Owen, "My subject is War, and the pity of War. The Poetry is in the pity."
Perhaps the best known works by both poets are "Dulce et Decorum est," "Anthem for Doomed Youth," and "Insensibility," all by Owen, and "The Poet as Hero," "The Death Bed," "Attack," and "To Any Dead Officer," all by Sassoon. These poems deal with the horrors of trench warfare, satirize patriotism, and denounce the propaganda used to sell the war to the public.
With this in mind, perhaps your paper could then argue how the poems provide a realistic portrayal of the war versus the public perception? How poetry and the arts can be used as commentary on the horrors that governments try to spin? You could also argue that writing poetry can be therapeutic for those suffering trauma, as these writers were said to suffer from "shell-shock" (now known as Post-Traumatic Stress Disorder (PTSD)), which greatly influenced their work.
Keep in mind that an "argumentative" essay simply needs to illustrate a key point (your thesis) and defend it with specific and clear support.