From the inside flap of the 1960 Ace edition
Vulcan 3 was the supreme head of unity, the perfect world government that has evolved out of chaos and war. Vulcan 3 was rational, objective and unbiased... as only a machine could be!
Theoretically there should have been nothing but peace under such a rule-and for a century or so there was. Until the crackpots, the superstitious, the religious fanatics found themselves a new leader to follow.
Then the discontent began to explode again. But this time there was a third side involved, a machine that could not accept any emotional of viewpoints. The people of the world began to realize that they had created a vicious paradox: they had to make peace between themselves or be stamped out by the ever-growing claws of Vulcan's Hammer.
From the back cover of the 1972 Ace edition