What is the major conflict in Oedipus Rex?

In literature, conflict can be defined as a struggle between two opposing forces.  This conflict can be external (between two characters) or internal (within one character).  In this play, there are many possibilities as to what the main conflict.

You could say that it is Oedipus's internal struggle against the idea that he is responsible for the plague. You could say that the major struggle is between Oedipus and Tireisias and Creon since they say he is the cause and he doesn't think he is.

My opinion is that the conflict is more abstract -- that it is a conflict between people and their fate.  I think that the play is about Oedipus's struggle against a fate that was preordained for him.