According to mythology, mankind used to live in 'The Tranquiline Halls': heaven. But then the Voidbringers assaulted and captured heaven, casting out God and men. Men took root on Roshar, the world of storms, but the Voidbringers followed. The Almighty gave men powerful suits of armor and mystical weapons, the Shardblades. Led by 10 angelic Heralds and 10 orders of knights known as Radiants, mankind finally won (or so the legends say).
Today the only remnants of those supposed battles are the Shardblades, the possession of which makes a man nearly invincible on the battlefield. The entire world is at war with itself - and has been for centuries since the Radiants turned against mankind. Kings strive to win more Shardblades, each secretly wishing to be the one who will finally unite all of mankind under a single throne.