Dark War
A historical conflict, which by inference in Unseen Academicals is not as far back in antiquity as a lot of people might like it to be.
According to the text of Unseen Academicals, "No one could have been neutral when the Dark War had engulfed Far Überwald". A sideways reference to Tolkien's Middle-earth, perhaps, especially in the light of Mr Nutt's species and their perceived role in the Dark War of antiquity.
"Neutral" is also a third option in Dungeons and Dragons when it comes to the whole vexed business of characters declaring their personal preferences viz, preservation v destruction, slaughter v salvation, Good v Evil or Law v Chaos. "No one could have been neutral ..." tells us that in the Tolkien mind-set, there were no other options but good or evil. It was axiomatic that you declared for one or the other with no space for any sort of prevarication or grey area. It took a later thinker and fantasy writer, Michael Moorcock, to redefine the primal categories not as Good and Evil but as Law, Chaos, and the neuter state Neutral. This allowed for a whole pallette of subtler and less two-dimensional characterisations - ie, being of the Law doesn't mean you necessarily have to be good (example: the Auditors), and being of Chaos is not automatically evil (example: Mr. Soak). It is interesting that Gary Gygax, founder of D&D, chose to take his cue from Moorcock rather than Tolkein, as the Moorcock system offered infinitely greater possibilities.
"Alas, when the time came to write down their story, his people hadn't even got a pencil". Unlike more favoured races who had time and liberty to craft entire Red Books of Westmarch to get their side of the story out first... the Dark War is referred to on page 58 by Vetinari and on page 60 by Mustrum Ridcully, where Vetinari likens the playing pieces on the Thud board to the Dark Hordes, in their lack of free will and their having been crafted for a single purpose - to fight. Ridcully reflects on what "the monsters" had been bred to do, and wonders what became of the thousands upon thousands of them who were bred to fight. (This might be a nod towards the many hundreds of thousands of wargaming figures crafted in the wake of the LOTR movies, and the Games Workshop "Warhammer" fantasy rule system...)
Also, re-referencing Middle-earth, Treebeard speculates that Saruman had crossbred Orcs and Men, which he calls "a black evil", to create the Uruk-hai, perfect fighting machines to fight in a war that engulfs a large area of land... Vetinari himself notes that it wasn't Igoring goblins that produced orcs, but using humans, in whom the natural capacity for violence and evil is so much greater. There's also a slight resonance with the original Tolkien orcs who were not part of natural creation, but later made and corrupted (from Elves or Men, various unpublished theories). In neither case are they natural creatures - they have been twisted into these shapes through evil intent.
It is possible that Lady Margolotta is a surviving eye-witness of the Dark War and may have held higher office in the Unholy Empire than she cares to admit today. It is also possible that the modern-day Code of the Igors is a result of their genuine repentence at what the clans helped to inflict on the world in that time.