Originally Posted by
kjn
I'm focusing on the Amazons here: they are the daughters of Demeter, and were charged by her and Artemis, Hestia, Aphrodite, and Hermes to teach mankind about justice, civilisation, and loving authority. They founded the first city of Themyscira by the river Treme in modern Turkey, but they also traveled the world to teach and learn.
The first generation of Amazons were very long-lived, but they also gave birth to daughters who they raised. The boys were given in the care of their fathers. Themyscira was otherwise closed to men, except that they were allowed to live there for a limited time in certain quarters. The Amazons turned into outstanding scholars and artisans, and many of them had talents as seers.
After Theseus and Heracles conquered Themyscira, and the Amazons freed themselves, this also had repercussions with the gods of the Olympos. Athena, who earlier had been neutral to hostile to the Amazons, was angry over the behaviour of Heracles, while Zeus was angry at them over killing/defeating/humbling Heracles. The Amazons were charged with protecting a several important artifacts and retreated to their current island, also named Themyscira, where they built their new city.
Many of the Amazons were pregnant when they arrived at their new island, including Hippolyta. The daughters they raised, while the boys were given in the care to Hermes and Artemis. That included Hippolyta's son, her first-born child. She prayed to the goddesses for help, and they told her to sculpt a daughter from clay. Thus Diana was born as the youngest of the children born on the island, though by less than a year than the next youngest one. Unbeknowst to her mother, Diana was also blessed by the goddesses with different powers and abilities.
While on the island, the Amazons who arrived there were sworn never to leave the island or face Zeus' wrath. However, the Amazons born on the island were free to leave it. While on the island, the Amazons are immortal, but if they leave it they become mortal though aging slowly.
The Amazon society is small and nurturing, but not without tension. Some of the Amazons broke away from the deal with the gods, and formed the Bana-Mighdall; they were pursued by the wrath of Zeus until they could reach a refuge in a far-away country. Those Amazons who were away from away from the first Themyscira when it was conquered were cut off, most integrating with Man's World, but some managed to join the Bana-Mighdall. Within Themyscira, there are different opinions on the view of men, on theology, but also based on simple personal animus.
Most of the time, Themyscira is magically shielded and inaccessible from the world, but at times it connects with different places, leading to the island having a very varied flora and fauna. It is always possible to leave the island, however, but often with little control where you end up. At times shipwrecked men have ended up on the island, they have been brought to a small island just off the main one, nursed back to health and released back to the world to tell fantastic tales.
When Steve Trevor crashed on the island, he however told tales that Man's World was a very different place, and the Amazons received omens that it was time for them to take a more active role in the affairs of men. Thus the choice to hold a contest to choose their emissary. Meanwhile, Amazon artisans repaired Steve's plane, turning it invisible in the process. Diana took part in the contest, against her mother's wishes, and won it. She was charged, according to the old tradition of the Amazons, to teach and learn in Man's World. To get back to Themyscira one of the pegasi living on the island is charged with seeking her out when the island becomes accessible, and bring her and her new-found knowledge back.
I'd also make Steve Trevor a gay man, partly because of the humour value of having a gay man on a fantasy island populated by women, partly to give Diana greater freedom in seeking relations. Also, somewhere in Man's World Diana might have a half-brother that she doesn't know about, that is an old and painful memory to her mother and several other Amazons.