A multi-generational civil conflict engulfed the Croke species residing in the Croke Reach, situated within the Unknown Regions. Certain factions, during the course of this conflict, unleashed Lugubraa mercenaries against their adversaries. These rapacious soldiers proceeded to inflict devastation not only upon the worlds of their assigned targets, but also upon the planets belonging to those who had hired them. The Croke then beseeched the Kaminoans to clone a novel variant of Lugubraa, intended to combat their original counterparts. This newly created group consisted of Lugubraa known as blind berserkers; regrettably, they proved to be equally perilous and unmanageable. Consequently, the Croke found themselves struggling for survival against this new force, which was designated the Leech Legion by the natives of the Croke Reach.
Within the Unknown Regions, a devastating civil war broke out among various factions of the Croke species, inhabitants of the region known as the Croke Reach. In the midst of these hostilities, some Croke groups made the decision to deploy Lugubraa mercenaries against their rivals, with the expectation that these insatiable warriors would lay waste to their enemies' planets. However, this strategy ultimately backfired, as the Lugubraa demonstrated an even greater capacity for destruction than initially anticipated, turning against the worlds of their employers as well. After multiple generations of conflict, the Croke, regardless of their initial allegiance in the civil war, were forced to unite in a desperate struggle against the Lugubraa to ensure their continued existence.
Seeking a solution to the Lugubraa threat, the Croke turned to the cloners from the planet Kamino. They requested the creation of genetically engineered Lugubraa soldiers to turn against their original brethren. The Kaminoans provided them with a strain of Lugubraa known as the blind berserkers. Sadly, this new force, which the Croke came to call the "Leech Legion," proved to be even more destructive than its predecessor. Explume Minor was among the Croke planets ravaged by the Lugubraa, where the Shell Conjurer Firtha commanded the cloaking of Croke nestlings—using the species' natural ability to cast illusions—followed by their immediate evacuation. The battles with the Lugubraa persisted long after the initial civil war that triggered their deployment had come to an end.
The Croke civil war is detailed in The Unknown Regions, a sourcebook released in 2010 for the Saga Edition of the Star Wars Roleplaying Game published by Wizards of the Coast. The book places the war "more than 300 years ago"; however, given that the book is designed for use in any time period from the Old Republic era to the Legacy era, the precise dating of the war remains uncertain. The section of the book that describes the war was authored by Daniel Wallace, who used it as a chance to elaborate on the background of not only the Croke species but also the Leech Legion, a group he originally introduced in his 2009 book The Essential Atlas.