"Dulce et Decorum Est" creates a sharp and deeply ironic line between the civilians who prop up war efforts and the men who fight their battles. As Owen suggests, there's almost no way for either group to understand the other. Only those who have experienced the horror of battle can understand the trauma of losing a fellow soldier. Ironically, however, these soldiers don't have the ability to communicate fully with those at home who could bring the war to an end – the people who reiterate old slogans about honor, duty, and patriotism without ever having to experience the terror of battle themselves. The very word "war" begins to mean two very different things for the two populations in this poem. Tragically, these views seem increasingly irreconcilable.
Through emphasis on the hellish, nightmarish quality of gas-attacks, Owen suggests that war itself is a vain dream.