Edward Llewellyn-Thomas (1917- 1984) had a long and interesting career. Two elements of that career warrant inclusion here. The first is that towards the end of his life, he began writing and publishing science fiction under the pen-name Edward Llewellyn. The second is that he was a Professor in the University of Waterloo’s Psychology Department, something I only discovered while reading his obituary in 19841.
1984’s Salvage and Destroy is the fourth book in his Douglas Convolution sequence.
The Ult have ruled the Cluster for millennia, ever since the Drin, former masters of the Cluster, made the terrible mistake of contacting the then-barbaric Ult. Extermination denied the Drin the chance to learn from their error; the Ult, now the most civilized of civilized races, remember how they came to power. They will never make the mistake of handing a youthful barbarian race the keys to the stars.
Their compulsively altruistic Ara cousins, on the other hand, could not leave well enough alone. Which gets us to the matter of the humans.