The longest pbm game I have ever been in was run by Bruce Douglas. I played in it for some 25 years, from 1983, but it folded permanently when Bruce became seriously ill. It started long before this as a tabletop game with figurines on bases. The players were all locals in Northumberland. Also in The Known World was Phil Barker, who was a major developer of game rules by The Wargames Research Group.
This is nothing to do with the novel of the same name.