Dungeons and Dragons: Krystallos
The details vary from people to people but the origin story of Krystallos remains basically the same: There was nothing until the totems came and planted themselves in the void. From the totems grew the land and the skies and the seas. Then, they rescued life from dying lands elsewhere and brought them to populate this new world. Since that time, the people brought to Krystallos have created nations and tribes and cultures and customs. Roughly a century ago, invaders bubbled up from portals located deep beneath the ground in the south of the Kingdom of Opal. A strange combination of different creatures and previously unknown races all led by a being known as Tiamat. Opal was quickly conquered and the invaders spread into Krystallos at large. The war raged for nearly a decade but, in the end, the combined forces of Krystallos managed to push the invaders back into Opal and then back further, into the tunnels. Legend states that a group of unknown heroes, known only as the Champions of Krystallos, traveled into the tunnels beneath Opal and sealed the portals leading to the home of the invaders at the cost of their own lives. Since then, the world has moved forward and the war has been almost forgotten. Only the elves and dwarves live long enough to remember the war personally. However, the war has changed the world in ways that are still being felt.