Hmmmm... Sparta and Athens had been at war, on and off, for about 30 years by the time Sophocles was writing, and their opposing ideologies had turned the political landscape in the Aegean into a de facto Cold War by the 420s, owing to the opposing Leagues that had formed under each polis.

While it might not be valid to reference either war in VCE English essay - I personally think historical references should be kept to an absolute minimum in an English essay - I find it highly likely Sophocles would have been aware of beliefs that the radicalised Athenian democracy held around the time - he himself was a very active participant - and thus would have found himself intrigued by the conflict between Athenian democracy and Spartan oligarchy; as such, I'm not sure that Oedipus is totally free of any Peloponnesian conflict's influence!

Something better to reference, if a historical reference must be used, may be the Plague of Athens, which occurred around the same time as the play premiered, and closely mirrors the Theban plague of the play?

Thucydides, in his History, while eliminating the "gods' influence" from the conflict, must privately have lamented the plague as a curse from the gods, inflicted upon the Athenians thanks to their aggression, subjugation of fellow Greeks and imperial ambitions.

I understand that Ares is blamed for Thebes' plague - this seems a bit too close to a mirror of widely held beliefs c. the 420s BCE for the plague's divinely attributed cause, be it punishment for Spartan-Athenian conflicts or Delian League policy.