Long ago, when humans and halflings were still new to the world, the came a darkness known as The Scourge. Strange man-spider creatures swarmed over the world destroying everything in their path. All the races retreated to their strongholds. The humans to their strongest castles,the dwarves dug deep underground, the elves fled to the deepest forests, eladrin to the feywild, the halflings to the sea, the orcs to mountain layers, and the dagonborn to their citadels, the minotaurs to their mazes.
When things were at their darkest, Solace the sun god chose a champion. The champion traveled the world and found a champion from each of the races to be imbued with their gods powers. Together they managed to find the Queen of the man-spiders and kill her, ending the Scourge, though at the cost of their lives.
Such horror, and such a heroic sacrifice built solidarity between the races. There has at times been tension and war in the world, but the mutual respect gained all those years ago helped usher in an age of relative peace and prosperity.