Bibblings is a novel written by Barbara Paul. It was first published in 1979.
An energy-providing ore, much needed by a federation of populated worlds, is present in abundance on a distant planet called Lodon-Kamaria. But no attempt has ever been made to mine and export the ore, because the Lodonites and the Kamarians are in a perpetual state of war. They can't even agree on the name of their planet.
Federation Headquarters sends in a diplomatic team to see what can be done. They touch down first in Lodon...and are shocked to find that the entire nation is mad. The army is a shambles, the leaders are as insane as those they try to lead, and the place is dangerous. The Lodonites have little or no awareness of what they're doing.
The diplomatic team retreats to Kamaria...where they find a sane, civilized nation with a disciplined army under the command of a capable general. So why haven't the orderly Kamarians been able to defeat the madmen they are fighting?
The answer comes soon enough, when the Kamarians gradually begin to go mad themselves. The Lodonites, however, have recovered their sanity and are beginning to rebuild their world. It's up to the diplomatic team to find the cause of this seasonal madness...even when they learn they are susceptible to it themselves.