The story of the Trojan War begins with the hero Peleus, one of the Argonauts. Twice he killed one of his own relatives and was banished. Eventually, he came to be the king of Phthia. As a reward for his great deeds in spite of bad fortune, Zeus gave to Peleus a new bride, the goddess Thetis. Prometheus had prophesized that her son would overthrow Zeus, and so Zeus wanted nothing to do with her, although she was very attractive. To solve the problem, Zeus married Thetis to the hero Peleus. This way, she could only bear mortal children, who could not overthrow Zeus in Olympus.
The wedding of Peleus and Thetis caused the Trojan War. Zeus invited all of the gods and goddesses, except for one, to come to this wedding of a hero and a goddess. The only one he did not invite was Eris, the goddess of strife/disharmony. To get back at the gods for this insult, she, of course, caused strife. She threw into the wedding a golden apple, with 'To the Most Beautiful' written on it. The three most powerful goddesses, Hera, Athena, and Aphrodite vied for the apple.
Obviously, no man in his right man would agree to be the judge of such a contest. Eventually, however, they found Paris, a prince of Troy, who agreed to judge. Each goddess attempted to bribe Paris. Hera offered wealth and power, Athena offered military greatness, and Aphrodite offered the most beautiful woman in the world. Paris chose Aphrodite, assuming that the most beautiful woman in the world was in fact Aphrodite herself. After the judgment was handed down, Aphrodite informed Paris that she is a goddess, not a woman, and the most beautiful woman in the world was Helen of Sparta.
Paris then headed off to Sparta to claim his prize. In Sparta, Paris was entertained by king Menelaus, the husband of Helen. Menelaus, however, soon had to leave for Sparta, and he instructed his wife Helen to entertain their guest. As soon as Helen looked upon Paris, she fell madly in love, because of Aphrodite. When Menelaus returned, the two lovers were forced to flee. They grabbed whatever valuables they could find, and sailed for Troy. Compelled by honor, Menelaus went to his brother Agamemnon, the king of all the Greeks. He gathered up a great army and 1,000 ships to get Helen back.
Euripides. Trojan Women.