Circus World

From back cover of Berkley paperback January 1981:

A PLANET OF DREAMERS AND CLOWNS VERSUS THE BEST MILITARY ACT IN THE GALAXY!

When the circus ship City of Baraboo crashed on Momus, the troupers of O Hara's Greater Shows turned a rockpile world into a showcase of razzle-dazzle. Generations of mimes and acrobats, barkers, and freaks, fortune-tellers and magicians built a new civilization based on showmanship.

Then the Vorilian Council of Warlords decided that the circus world was a prime spot for a garrison and brought in an armada to "liberate" Momus.