What is the Iliad about?

The Iliad is an epic poem written by Homer. Its subject is the Trojan War, a war between Ilium (or Troy) and the Greeks (often referred to throughout the poem as Achaeans). The conflict starts because Paris, one of the sons of Priam, King of Troy, takes part in a competition to judge who is the most beautiful goddess. Aphrodite, goddess of love, offers Paris a woman named Helen, the most beautiful woman in the world, if he chooses Aphrodite. He subsequently complies. Unfortunately, Aphrodite neglects to mention that Helen was already married to Menelaus, King of Sparta.
Paris, overcome with lust, abducts Helen from Menelaus's palace and takes her back to Troy. Menelaus, not surprisingly, is outraged. His wife has been taken and his kingly honor impugned by this young Trojan upstart. Also, Helen's many suitors took a vow to defend her when she was married. So kings and warriors from across the Greek world join forces to converge upon Troy, ultimately to do battle there for ten long years.