What is the main problem afflicting Thebes at the beginning of "Oedipus Rex"?

The primary issue that Thebes faces at the beginning of "Oedipus Rex" is a plague. This affliction manifests in widespread suffering, including disease, death, and despair among the citizens. The severity of the situation compels the residents to seek help from their ruler, Oedipus, who is depicted as a proactive leader willing to take on the responsibility of finding a solution. The moral and physical decay caused by the plague sets the stage for the unfolding tragedy, as Oedipus strives to uncover the truth behind the afflictions plaguing his city. The plague is not just a simple backdrop; it serves as a catalyst for the central themes of fate, identity, and the repercussions of knowledge that permeate the play.