What was the background history that initiated the Trojan War?

Eris, the goddess of discord, became angry when she wasn't
invited to the wedding of Achilles' parents. As revenge, she threw a golden apple that
had "for the fairest" written on it into the hall where the wedding was taking place.
All the goddesses felt the apple was theirs, but the decision came down to Hera,
Aphrodite, and Athena. The three wanted Zeus to decide, but he knew better and sent them
to Mount Ida where Paris, the prince of Troy, was living, for Paris to decide among the
three. All three try to bribe Paris, but he chooses Aphrodite, making the other two
goddesses very angry. They vow revenge against Paris for his decision and make him fall
in love with Helen, the most beautiful woman on earth, and the wife of Menelaus, the
king of Sparta. When Paris visits Menelaus,  he and Helen run away to Troy, taking most
of Menelaus' treasure with them. Menelaus convinces the other kings to go with him to
Troy to avenge the dishonor and embarassment Paris had caused him and to retrieve Helen.
The war cost many lives, lasting twenty years.