THE THREE-WAY WAR
More than a million years ago the Three Galaxies were dominated by several powerful ancient alien races: the Landru, the Hur'ruk'ru, and the Krang. Eventually these militant empires came to blows, and over a few millennia wiped each other out. All were slaver empires, forcing sentient beings across the galaxies to do their every whim, but the Landru were different: they didn't see their minions as "throw away" like the other two races did. Sadly the Landru were the least militant of the 3 races and they perished early in the conflict. There is an ancient rumor that the Landru, in a last desperate act, mass teleported many of their slave species to a hidden Dyson Sphere, to preserve them against the galactic fighting that was at the time raging across the Three Galaxies. However, that Dyson Sphere has never been found.
No one truly knows why this Great War began, and rumor and speculation in old taverns and universities spread across the Three Galaxies has never resulted in any real, tangible evidence of the cause of this galaxy-shattered war. Some say it was the aggressive and expressionistic Krang that initiated the whole mess, while others was sure that it was the xenophobic Hur'ruk'ru that sparked the ultimate fire that consumed hundreds of worlds. All that is known for sure is that the less militaristic Landru was caught in the middle of the conflict and perished first.
The remains of this great war is strewn all across the Three Galaxies, from still-functioning automated weaponry and AI-driven warships to crater-ridden worlds and immense asteroid belts that were the former homeworlds of hundreds of races allied to the Big Three: the Landru, Hur'ruk'ru, and the Krang.
THE KRANG
The Krang were the most militant of the three races, brutally enslaving thousands of other alien species within their domain and crushing any resistance with genocidal tactics. Their weaponry were specialized in the fields of exotic matter (including protomatter) and they were superb physical warriors, defeating any and all comers on the battlefield. Eventually the Hur'ruk'ru detonated a massive black hole device in the center of the Krang Empire, utterly destroying it while the Krang later retaliated in kind with their protomatter warheads, seeding the central stars of both the Landru and the Hur'ruk'ru with star destroying weapons.
THE HUR'RUK'RU
The Hur'ruk'ru were extremely alien in their outlook on life, having evolved inside the hydrogen winds of enormous gas giants. They were noted as powerful master psionicists and were especially cruel towards humanoid races within their area of space. They were often bizarre in their physical behavior and they used their mental powers to crush entire worlds, bringing numerous alien races under their control in short order. Those they could not dominate, they wiped out completely and utterly. The Hur'ruk'ru outlasted most other races during the Great War before finally being exterminated by the infuriated Krang.
THE LANDRU
The Landru were a hexapod race that were very alien in their thinking, since they had evolved five segmented brains and three pairs of eyes. This alien herd-race treated its slave species very well compared to the other two major powers at the time, except for carnivorous races, which they kept in forcible isolation on low-tech worlds. Not well equipped for war, they were almost immediately on the losing end of the Three Way War and passed into history nearly a million years ago.
