What are the causes of war in The Knights by Aristophanes, if any are specified?
The Knights by Aristophanes is a political satire that attacks populist demagoguery, especially that of Cleon, who appears as "the Paphlagonian" in the play. Although the play is comic, and has fantastical elements, as with most of Aristophanes' dramas, it makes a serious point about the causes of the Peloponnesian Wars.
The main thrust of the play is critique of the "demos" (personified as Demus) and the way popular demagogues such as Cleon flatter and pander to the mob, instead of doing what is best for Athens in the long term. Aristophanes' criticism is based in part on an objection to Athenian imperial ambitions, which he sees as rooted in the greed of the demos (and the aristocracy) for luxury, necessitating a foreign policy that was closer to colonial exploitation (or even looting) than diplomacy, and land grabs and excessive liturgies to finance foreign wars.
The treatment of oracles also satirizes the superstitions of the mob, and the way demagogues would abuse the oracles and other religious traditions to gain power. Although the treatment of the war is not foregrounded in Knights the way it is in some of Aristophanes' other plays such as "Peace" and Lysistrata, Knights is a strong attack on Cleon, who was the most hawkish of warmongers and leader of the populist party in the period.