What do Aphrodite, Hera and Athene fight over that is essentially responsible for starting the war in the novel, A Thousand Ships?

Aphrodite, Hera and Athene fight viciously over the golden apple, and in doing so they start the Trojan War. The apple is a symbol of how overwhelming personal vanity and greed can tip the world into chaos: these almighty goddesses, who have such power at their fingertips, nevertheless focus their immense attention upon the acquisition of a gaudy bauble.