The novel's epigraph initiates the intent to further allow the reader to learn about the mental damage that the First World War imposed on soldiers. When Paul speaks about his entire generation "destroyed by the war-, he is talking about the way him and all of the other young soldiers becoming less and less human. The major psychological impact brought upon these young men wreaked havoc with their mental health after the war, even if they survived physically unharmed. .
Most of the soldiers that served the armies throughout Europe were very young, and at that early age, most of them felt like their life had already ended. Prior to WW1, wars were generally not fought nonstop over the course of years, and that most of the soldiers in previous wars were professional mercenaries and war veterans. Now that this Great War is the complete antithesis of wars in the past, it had a profound effect on the minds of young men. They all felt like it was a patriotic duty, instead of a career when serving for their army. This was because the war was born from nationalism.
During this war, soldiers found themselves in utter boredom sitting idle in the cold, dirty trenches. The monotony was so intense, that soldiers began to feel detached from themselves and from human nature. They have become droning zombies that merely exist to prolong this state of war, and they don't feel as compassionate about their fallen comrades as they do about their next meal. When the cook makes a surplus of food, the cook doesn't think about the soldiers who have died. He doesn't acknowledge their existence; he only cares about whether or not if he should give the soldiers the extra ration. He obeys the rules rather than thinking of what to do morally. Humans tend to give much thought and compassion for their sick and deceased kin, but as seen in the trench of Europe, all morals have become lost. Therefore, Paul's generations of young men are doomed to an inevitable mental alteration.