In the ancient past, the Immortal Dao flourished. Immortals could roam the Great Void, live forever, and wield powers that reached the heavens and earth.
Then came an ancient war between immortals. The Immortal Realm shattered, the Immortal Dao was severed, and the spiritual veins were cut off.
The human world today is called the Canglan Realm: a remnant cultivation age in the era of the end of the law.