How is the theme of social/political change on individual life portrayed in "The Waste Land" by T.S. Eliot?

T.S. Eliot's "The Waste Land" was published in 1922 and reflects the unease and disillusionment in society after the horrors of the First World War. The effect of this war in particular upon the individual is marked in the poem: the war occasioned enormous social and political change, but also made doing the simplest things difficult for those who had gone to war and then been forgotten by the government they served. In this poem, Eliot moves between classical allusions and narrow focus on everyday scenes, a technique which emphasizes the sense that the world is now somehow ill-fitting—or rather, that those who once belonged to it now fit in it poorly.
The poem begins with allusions to Russia and France, but settles on its main social focus, London:

A crowd flowed over London Bridge, so many,
I had not thought death had undone so many.


But the deaths of others have certainly undone many in London. Eliot shows the fragmented conversations of men who, we understand, have returned from the war with shell-shock:


“My nerves are bad tonight. Yes, bad. Stay with me."
. . .
I think we are in rats' alley
Where the dead men lost their bones.

The conversation is clipped, erratic, and betrays the deep desire of these people for a connection which now seems out of reach, and a certainty which has been lost:


“What are you thinking of? What thinking? What?
“I never know what you are thinking. Think.”

By contrast to these anxiety-ridden, clipped words from the returning soldiers, the women in the poem speak in a stream-of-consciousness flow which mimics real life and yet is so far removed from the men's speech that it marks the disjunction between the two. Those who did not experience the war can no longer connect with those who did; society has been riven by this event.

When Lil’s husband got demobbed, I said—
I didn’t mince my words, I said to her myself,
HURRY UP PLEASE ITS TIME
Now Albert’s coming back, make yourself a bit smart.
He’ll want to know what you done with that money he gave you
To get yourself some teeth.


The barman's refrain, "HURRY UP PLEASE ITS TIME," creates a sense of social realism and would have been relatable to the contemporary reader; moreover, however, it indicates that these people have stayed in the pub all evening, right up to closing time (midnight). They are seemingly unable to determine what to do with themselves.

There is a sense in this poem that every speaker is always on the edge of madness. Bursts of realism, such as the public house scene, are interspersed with dreamy reveries, echoes of death, which descend into fragmented allusions and nonsense:


White bodies naked on the low damp ground
And bones cast in a little low dry garret,
Rattled by the rat’s foot only, year to year.
But at my back from time to time I hear
The sound of horns and motors, which shall bring
Sweeney to Mrs. Porter in the spring.
O the moon shone bright on Mrs. Porter
And on her daughter
They wash their feet in soda water
Et O ces voix d’enfants, chantant dans la coupole!

It is as if the speaker cannot focus on one thing for any length of time, or perhaps seizes upon any possible distraction. What is certain is that he does not wish to dwell upon the rats to which the poem frequently refers, a motif representative of the decay in society. This society seems unlivable, impossible; and yet Eliot's classical allusions, at the same time, suggest that this is simply a cycle we all go through. An immortal, perhaps, would have experienced this kind of social disfunction many times:


(And I Tiresias have foresuffered all
Enacted on this same divan or bed;
I who have sat by Thebes below the wall
And walked among the lowest of the dead.)


"The Waste Land" is a long and hugely significant poem which you could spend many hours unpacking. For the purposes of your question, it also has a lot to yield about social and political change and the general discomfort in society at this time. You might consider also the question of "the third who walks always beside you"—who does this represent, and why?—and the way the poem breaks down to end in fragments in a foreign language.