World War I had a huge impact on people. We tend to forget about how devastating that war was because of the greater horrors of World War II. Before WWI, mass destruction of people and property just was not possible. With the "advances" made in weaponry during the war, it became possible to kill an entire battalion of soldiers with one canister of mustard gas or one volley of air fire.
Poets like Eliot became very disillusioned and despaired for the future. For him, the world had become like a waste land. What could anyone hope for in a world in which life is valued so little? The eNotes study guide tells us that "Eliot was rebelling against the tendency to glorify the past. He wanted to demonstrate that the past was gritty and real, especially the recent past events of World War I. By demythologizing the events of the past, Eliot forces his readers to focus on the grim realities of his postwar present."
The poem is difficult to interpret, but Ryan Pouquette notes that
the reader needs to be disoriented. Society has become too stale and exists in a state of living death, where crowds of these walking dead file off to work, exhaling “Sighs, short and infrequent.” Even the sighs of despair and disillusionment are “infrequent,” because this society is lost and does not even have the energy to sigh. Eliot is attempting to shake up society and get people to, as he notes during the second section, through the mouthpiece of the rich woman: “Think.”