Before we look at the texts in any detail, it is necessary to get an idea of where and how drama has developed.  There are a number of excellent sites devoted to this issue.

You might first want to look at the origins of theatre itself.  These links will take you back to the roots and early history of Greek theatre. Elsewhere you might want to explore tragedy through the ages.  It's a word that becomes obviously overused and less than precise when you consider what subjects come up from a cursory search of the web, from a Norwegian metal band to the misuse of the word in newspaper reports (not everything is a tragedy).  Finally, once you have a sense of the style and origins of Greek drama, you might want to look at some of the following responses to tragedy (an interesting, though not particularly well-proofed document), more closely and ask yourself how they apply to our tragic text,  Death of a Salesman.

But while the classical heritage plays a huge part in Western thought and Culture, we might also want to spend some time looking at the emergence of a theater steeped in the ritual of the church and taking the resolute step towards being characteristically English language based.

The European tradition traces its roots back specifically to the Mystery and Miracle plays that began as illustrations of Church dogma and became increasingly secularized and responsive to audience.  Look at this link for a very readable overview of the process.

For an example of early drama, take a look at one or two of  the medieval York Cycle of plays.  The clearly moral framework of such early drama might help us think about modern drama like Glaspell's "Trifles," though its gender theme self-consciously reframes the moral issues of guilt and judgement in the play.  Before you look at that, however, review David Ives' one act play, "Sure Thing," with its bare minimalism, and inventive dialogue, it's an interesting place to start.