udgement of Paris
The causes of the Trojan War actually began before the Greek hero Achilles was born.
The two powerful gods, Zeus and Poseidon try to forced sea-goddess Thetis to lay with them. Themis or Prometheus warned the gods that any son Thetis borne would become greater than his father, and in Zeus' case, would probably one day rule Olympus. That really dampened both gods' amorous pursuit of the goddess. Zeus decided to quickly marrying Thetis off to a mortal.
Zeus chose the hero Peleus, son of Aeacus, as the most worthy of mortals. All the gods and goddesses attended her wedding except Eris, goddess of discord. Furious of this slight, Eris threw a golden apple, inscribed "For the fairest", in the midst of the guests. The wedding was marred, when three powerful goddesses wished to claim the prize as the fairest: Hera, Athena and Aphrodite.
The three goddesses asked Zeus to be their judge. Wishing to have nothing to with the contest, Zeus directed Hermes to refer the arbitration to Paris, a Trojan prince, the young son of Priam and Hecuba.
Each goddess offered to reward him if he chose her. Athena offered to make him become a great hero or general; Hera offered to make him ruler of the richest and powerful kingdom; while Aphrodite offered him the most beautiful woman in the world in marriage: Helen of Sparta. Paris foolishly decided in Aphrodite's favour and awarded her the golden apple as the fairest of them all. Troy was to suffer the enmity of the two most powerful goddesses.
But Helen had many powerful Greek suitors wooing her in Sparta. So powerful in fact that her father Tyndareüs or Tyndareus (her real father was Zeus), king of Sparta, was afraid that anyone she chose, would offend the other suitors.
This problem was solved when the prudent Odysseus, king of Ithaca, advised the Spartan king, that each suitor must swear an oath, that they will defend the interests of whoever Helen chooses to marry. Any who refused to swear this oath, would not be eligable. All the suitors agreed and swore the oaths to accept whoever became Helen's husband.
According to the Catalogues of Women, Hesiod wrote what some of the leaders had offered to Helen – rich bridal gifts, such as bowls, cauldrons or tripods made of gold.
Helen chose Menelaüs (Menelaus) as her husband. Menelaüs was the son of Atreus, and brother of Agamemnon, the king of Mycenae. Menelaüs married Helen and Tyndareüs abdicated from the throne, leaving Menelaüs to become the king of Sparta.
(Odysseus knew that Helen would never choose him, but Tyndareüs helped the hero to win Tyndareüs' niece – Penelope, the daughter of Icarius and cousin of Helen. Odysseus defeated other suitors of Penelope in a foot-race and married the Spartan princess.)
At that time, Paris was living in Mount Ida with his wife, Oenone, a mountain nymph, but he abandoned her for Helen. Oenone told Paris if he was ever wounded that he should come to her, so she could heal him. Oenone had hoped that her husband would return to her.
Despite been warned by his brother and sister, Helenus and Cassandra, who were gifted in divination that his journey would cause the destruction of Troy, Paris sailed to Greece with his cousin Aeneas.
At Sparta, Paris became guest of Menelaüs and Helen. Aphrodite made Helen fall in love with the Trojan prince. When Menelaüs went to attend his grandfather's funeral in Crete, Helen ran off to Troy with Paris with most of the treasures in Sparta, but leaving her daughter, named Hermione, behind.