The Hand of Dominion

From the introduction:

Once there was the empire of Niv, the greatest in the world. Zulin, god of the Upper Air, bestowed a magic sword upon the first emperor, Mozar I. The sword was called the Hand of Dominion, and it signified that the wielder was the rightful ruler of the world.

The unconquerable Nivian empire later became slothful and degenerate. Zulin withdrew his blessings, and their tributary states began to break away. The Nivian emperors were only overthrown in a series of assassinations and coups. So many were killed in their sleep that it was known as the Long Midnight. It was during this time that the Hand of Dominion disappeared from history.