Several Mandalorian warrior clans clashed with the Ithullan species in a war circa 200 BBY, the conflict stemming from a narcolethe distillery. After achieving victory, the Aka'liit clan carried the fight to the Ithull homeworld itself. The Mandalorians first seized the planet's orbital stations, then systematically disabled planetary communications and power-beam arrays. With the cloudtop cities now darkened and defenseless, the Mandalorian forces raided them, destroying reactor bulbs and causing the cities to fall into the deep Ithullan Depths. This resulted in the near-extinction of the Ithullan race, an act considered by numerous galactic scholars to be the most reprehensible crime of that era.
Because the Jedi Council took no action in response to the genocide, a group of rogue Jedi Knights defied the orders of the Jedi Council and allied themselves with the Gen'Dai bounty hunter Durge in retaliation, and they assassinated the ruling Mand'alor, the leader of the Mandalorian clans, almost a century later.
The Ithullan genocide caused widespread discontent among Mandalorian soldiers who were disgusted by the rampant immorality of their peers. Jaster Mereel recognized this desire for change and, upon becoming Mand'alor in 60 BBY, established a new code of conduct for the Mandalorian warrior clans. Mereel authored the Supercommando Codex, a new ethical guideline for Mandalorians that dictated that those who wished to fight should behave as honorable mercenaries.