In the future, arrows will auto-snap upon contact with a shield.
The novel is a fix-up of the first five of van Vogt's Gods stories which originally appeared in the magazine Astounding. Author and critic James Blish observed that the plot of the Gods stories resembled that of Robert Graves' Claudius novels. Author and critic Damon Knight said that the plot was "lifted almost bodily" from the plot of "I, Claudius."
Oh, there's more; whoever wrote this entry really didn't like the book.
Galaxy reviewer Floyd C. Gale faulted the novel for its odd internal contradictions, in particular a scene where "a fleet of spaceships makes a strafing run over the enemy, loosing flights of arrows from point-blank range."
It's about Earth in the future after an atomic war had destroyed everything. (Of course.) Civilization has rockets and space travel and atomic energy, but they don't understand how any of it works.
Inspiration perhaps for the Pakleds, the most despised Trek aliens ever.