Imaginary Space II

All fictions happen in imaginary space. Even the fictional London, New York, Stockholm etc are not the same as ours. If there were no difference, then they would not be fiction. Alan Moore thinks that imaginary spaces literally exist but I think that he is objectifying subjectivity. Fictions exist in our language, shared texts and individual imaginations but not also in some invisible, incorporeal realm. 

We saw that there is a vast body of sf that shares premises (i)-(vi). Conventionally, stories set in this vast set of imaginary spaces either are instalments in some particular series or are one-off, stand-alone narratives. Authors could be freer to mix and match elements of different stories and sometimes do but usually they stay with the conventional distinction between series and non-series stories. 

Thus, both "The Longest Voyage" and "High Treason" by Poul Anderson are one-off stories that do not fit into his Technic History or into any other such series but nevertheless are recognizably part of that larger imaginary space, or set of spaces, that includes FTL and related premises.

I have a problem that will be familiar to other readers of sf and particularly of Poul Anderson. I remember a story by Anderson but not its title. I thought that the story was in a collection in my possession but now cannot find the story. There was FTL. Human beings had colonized extra-solar planets. One planetary population had mutated and now lacked normal human motivations. A naval expedition crewed by members of a master race and of a subordinate race embarked on an expedition. By clandestine prearrangement, the subordinate class mutinied and slaughtered their masters in space. When the action of the story moved back to Earth, we learned that the centre of political power was now in Africa. Does anyone know what I am talking about?