You might like to consider the ways in which the themes of absurdism and isolation and loneliness stem from the contemporary political events that were occuring at the time. In The Birthday Party, for example, the context in which Pinter was writing was one of intense alienation and isolation as the world suffered a Cold War that divided the world in two. There was great fear of a Third World War, which, thanks to the advent of nuclear technology, would spell the end of the world as we knew it. The 1950s were marked by a series of conflicts where the major powers in the Cold War used other countries as an arena to covertly fight each other, such as Korea. At the same time, the Space Race began, where both the USA and the USSR tried to show that it was more scientifically advanced than the other. Britain itself, once such a massive world player, continued its decline as other countries became more powerful.
The "Angry Young Man" was a phrase that was created through Osborne's play Look Back in Anger, but it is a phrase that can be equally applied to this play by Pinter. As we can see, themes such as anger, isolation and insignificance stem from world events as they were happening and in particular the fate of the common man trapped in the middle of massive conflicts that seemed to rob him of agency.