here whether the term "the Breakup" is used in any of Poul Anderson's Technic History texts. It is:
"'I don't believe complete records are left of every attempt at emigration and settlement made during the Breakup, but we do know quite a few were less than successful.'"
-Poul Anderson, Sir Dominic Flandry: The Last Knight Of Terra (New York, 2012), p. 310.
Fenross speculates. Maybe some early colonists reverted to barbarism during the Troubles, then worked their way back up to reduplicating some ancestral technology before outgrowing their more recently acquired "'...wild ways...'" (ibid.). Thus, maybe it was such a group that sacked Fort Lone on the planet Varrak? It wasn't but this does demonstrate some possible long term consequences of the Breakup, followed later by the Troubles.
Varrak was colonized but only part of it was terraformed and Fort Lone is its single town. The colonists "'...hunt axhorns in the mountains...'" (p. 316). Vor, three days away from Varrak by hyperdrive, was discovered by Cynthians but, more terrestroid than Varrak, was humanly colonized, becoming populous, wealthy and the capital of the ducally governed Taurian Sector of the Terran Empire. It is the Duke, based in the city of Gloriana on Vor, who, for his own reasons, is responsible for the raid on Varrak. This leads to a long narrative about the Taurian Sector, continued in A Knight Of Ghosts And Shadows.