Guardians of the Universe

Before they were Guardians, long ago thet were known as the Maltusian race. The Maltusians were obsessed with bringing order to the universr and thus founded the Manhunters which aren't robots in E27 but a brotherhood of bounty hunters from all walks of life (for instance Lobo is a Manhunter and J'onn J'onzz's title of Martian Manhunter actually means something. (Kate Spencer and Miss Martian are J'onn's deputies).

Anyway, the Maltusians still felt that the Manhunters could be improved somehow. When their research discovered the Emotional Spectrum, they thought this was the answer.

The ancient Maltusians built seven (or nine, if you believe the legends) Power Relays across the galaxy, each channeling a different light from the emotional spectrum and housing a different entity inside. With this power, the Guardians formed different corps of ringbearers who could harness this energy and used them to connect routes between their Relays, shaping out a massive empire that engulfed tens of thousands of star systems.

Over time, however, due to the distance between Relays, the empire became splintered in factions and a war raged on until the Maltusian empire was destroyed by civil war and invaders that acted upon this opportunity.

The only faction not consumed in this war was the Green Lanterns of Oa, who had been the empire's peacekeepers and refused to take sides in the civil wars and instead rallied around the closest systems surrounding Oa to fend off invaders.

As time went on, remnants the old Maltusian empire were taken over by the Collective, Apokalypse, the Reach, and others as the Green Lanterns could only hold onto a fraction of their former empire: Approx. 3600 star systems (or Sectors) surrounding Oa (Sector 0 or Sector Prime). For reference, the Sol System (and Earth) is Sector 2814.

The Maltusian Council on Oa allowed refugees from the old empire to take up residency in Sector 666, but their old rivalries carried over and eventually the Green Lantern Corps was sent in to quell the fighting. But that didn't happen.

A crazed team of disgruntled Manhunters who had lost their families from all the civil wars decided that the refugees of the old empire represented a diseased limb of the once great empire and decided to take matters into their own hands, igniting an experimental weapon into the star of Sector 666, causing it to go supernova and destroy all life in the Sector just hours before the Green Lantern battalion had arrived to calm the warring.

Hearing of the Massacre, Apokalyptan invaders advanced upon what was now known as Oan space. But the massacre had united the Corps and the 8000 Green Lanterns took a strand at the border.

Not interested in going to war with the 8000 Green Lanterns loyal to Oa, Apokalypse ceased their invasion. The Collective, Reach, and other would be invaders did likewise whem confronted with a united front.

Peace has been tense as the borders remain under constant guard, maintaining a strict demilitarized zone that taxes the resources of many border civilizations and the Corps alike.