The goddess of discord, Eris, was not invited. When she discovered this, she was furious. Eris arrived at the party and threw a golden apple that was to the fairest. Hera, Athena, and Aphrodite fought over it.
Zeus told Hermes to pick a mortal to decide which goddess gets the apple and title. The mortal's name was Paris. He is the son of Priam, the king of Troy Athena offered to make him victorious in every battle. Hera offered to make him ruler over men. Aphrodite offered to give him the most beautiful woman in the world. Paris picked Aphrodite's offer. He wanted Helen.
Helen was already married to the Greek king Menelaus. Paris went to their palace to claim his new wife. He kidnapped Helen and went back to Troy.
The Greeks wanted to avenge Menelaus and retrieve Helen. After 10 years of traveling to Troy, the Trojan War began. The Greeks were starting to lose until Odysseus, a Greek warrior had an idea. They built a giant wooden horse, hid inside, and left it at the gates of Troy. The Trojans brought the horse inside and the Greeks attacked. The Greeks were victorious.