As usual, quite a lot of ink and paper have been expended to explain what Aristotle meant by unity of action. We can glean some insight by looking at the 2 works he singles out for praise, Homer's 'Iliad' and 'The Odyssey'. The unity of action in 'The Odyssey' is clear cut and proactive: the protagonist, Ulysses, struggles to get home to Ithaca after the Trojan War. There are many adventures along the way, many colorful characters, but all the incidents arise or are directly related to the protagonist's struggle for a singular purpose, his unity of action: get home. 'The Iliad' is different. The entire epic is framed by the wrath of Achilles, the causes and devastating consequences for the Greek alliance. "Rage-- Goddess, sing the rage of Peleus' son Achilles, murderous, doomed, that cost the Achaeans countless lives". Achilles refuses to fight because he's been dissed -- his honor and dignity have been betrayed by Agamemmnon. The unity of action for the first 2/3 of the epic (by my page count) is...is... is... Achilles' sitting out the Trojan War in high dudgeon! The Iliad has many set pieces, a cast of thousands, super-heroes in abundance (Odysseus, Ajax, Hector), a beautiful casus belli (Helen) and all the Greek gods meddling from Mt. Olympus. And all of that is framed by the pique of Achilles and how it plays out for the fortunes of the adversaries. Only after the death of his beloved friend Patroclus does Achilles reverse his position (literally and figuratively) and resume fighting. And then he goes on a murderous rampage, utterly beserk -- war rage! From first to (almost) the last, the story is driven by one issue only: the anger management problem of the legendary Greek super-hero, Achilles.

Doh! Meant to post in the discussion of The Poetics.