Waiting for Godot was written precisely after the World War II, and it is a commonplace to link the Theatre of the Absurd with the postwar trauma and disgust, a somewhat attempt to get rid of an acute sense of shame.
However, the main themes of the play are rather controversial and questionable. We may admit that, among other things, Beckett thoroughly focuses on the subject of power. More precisely, it is about power and interdependence -- the complex relation between master and slave (it is clearly evident on relations between Pozzo and Lucky). Who suffers more master or slave, who is more dependent and more vulnerable?
"I am asking you if we are tied? -- Tied? but to whom? by whom?"
Beckett raises a question: how can a man crave for his slavery as it was a sort of salvation? ("why doesn't he make himself comfortable? -- he doesn't want to", "do you want to get rid of him? - I do"). Do the characters seek the salvation from an unbearable sense of absurd (endlessly waiting in vain for something they are not even sure exists) in such queer interdependence?
We witness two pairs of gentlemen with very complex and odd long-term relations (50-60 years) ("There are times when I wonder if it wouldn't be better for us to part", Estragon tells Vladimir). In addition to interdependence, Beckett also highlights the theme of fate: what if our lives were completely different if we never met? ("when you think of the beauty of the way") Would not it be more rational, more successful?
In the afternoon of their lives, they have neither expectations nor hopes, they morally prepare themselves for death. The only thing that keeps them alive and gives them a reason is this waiting for Godot, which may be a sort of invented illusion to carry on. Beckett depicts a life routine as this waiting for Something (something great, something of high importance, that will turn our lives and end all "this circus"), but this something is always postponed, always hidden, 'nothing ever happens' ("What do we do now? -- Wait? -- But while waiting? -- What about hanging ourselves?"). When Lucky begins to "think aloud", everything is muted after the word "existence", then there is a nonsense declamation mainly built on formal meaningless phrases, that repeats "left unfinished for reasons unknown".
The play is Beckett's invitation for the audience to think further and introspect on their lives: what are their expectations, to what extent they are dependent, who do they choose for companions in their way, will not they be disappointed in the end of it, will not they be disappointed anyway, how should they prepare themselves for this etc.