Mandalorian–Ithullan war

Several Mandalorian warrior clans engaged the Ithullan species in a war over a narcolethe distillery in the year 200 BBY. After claiming victory over their foes, members of Aka'liit took the fight to Ithull itself. After seizing the planet's orbital stations, the Mandalorians blacked out planetary communications and deactivated their power-beam arrays. The now helpless darkened cloudtop cities were then raided by the Mandalorians, splitting their reactor bulbs and plunging the cities into the fathomless Ithullan Depths, resulting in the near-extinction of the Ithullan race; which a number of galactic scholars viewed as the most heinous crime of its era.

Because the Jedi Council did nothing in response to the genocide, a group of rogue Jedi Knights, in retaliation, allied with the Gen'Dai bounty hunter Durge against the orders of the Jedi Council, and assassinated the ruling Mand'alor, leader of the Mandalorian clans, nearly a hundred years later.

The genocide of the Ithullan species led to a large number of Mandalorian soldiers growing dissatisfied with their out-of-control, immoral contemporaries. This desire for change was taken to heart by Jaster Mereel, who instituted a new standard of behavior for the Mandalorian warrior clans when he rose to the position of Mand'alor in 60 BBY. Mereel authored the Supercommando Codex, a new standard for Mandalorian ethics, which stated that any Mandalorian who wished to fight were to conduct themselves as honorable mercenaries.

Text and facts from the “Mandalorian–Ithullan war” article on Wookieepedia, licensed under CC BY-SA 3.0. Modified for this site.