The Dark War was the intergalactic war instigated by Malduke in 75,000 BBY.
An upstart and Death Child named Malduke decided that the time had come for the Kajeat to claim their rightful place as leaders of the intergalactic community. He led a rebellion among the Kajeat and the other races, using his remarkable powers and abilities to lure millions to his cause. When the rest of the Kajeat and the intergalactic community attempted to shut down the rebel's efforts, Malduke resorted to violent uprising, and instigated what came to be known as the Dark War. In 75,000 BBY, he began proliferating weapons and technology to many of the younger races throughout different galaxies, including Humans, Duros, and many others. Soon, he had billions of ships and quadrillions of troops at his disposal. Furthermore, he had one ultimate weapon that gave him an advantage above all the others: he developed a weapon that could kill a Kajeat for good.
The Dark War lasted for centuries and caused devastation that reached across every sector of the intergalactic community. Countless systems were destroyed and races were wiped out. In addition, many Kajeat died, killed by Malduke and his unstoppable weapon.
Eventually, the Kajeat and the other races were able to destroy his weapon and defeat Malduke's forces. Taking him into custody, they faced a choice: rebuild Malduke's weapon and kill him with it, or find another way to prevent him from ever gaining power again. In the end, they decided to exile the evil Kajeat forever. Imprisoning him on a remote world in Epsilon Sector, the intergalactic community constructed the Galbagos Nebula to prevent anyone from finding and releasing him.
By this point hundreds of races had received technology from Malduke that might otherwise have taken them millennia to develop. In an attempt to rectify the damage Malduke had caused, the Kajeat and the intergalactic community stripped the younger races of all the advanced technology they had received, erasing all evidence that the Dark War had ever occurred. From that point on, the Kajeat vowed that they would never again interfere with the development of other races. They then became known as the Travelers, devoted to recording and observing all events in the universe, but never acting to affect those events again.