Their world was a beautiful blue watery globe, near a warm sun.
They had the technology to extract all of their energy from their planet.
And they had the technology to gather all of their energy from the sun.
Their economic model, based on the concepts of profit and debt, kept them locked into extracting all their energy from their planet, in eternal competition with one another, and all life on their planet.
As energy resources grew more and more scarce, the less aggressive majority, died.
Only the most aggressive survived.
Until they couldn’t see any other way than their way of doing things, always enslaving the less aggressive, to do what they ordered.
Eventually they began to geo-engineer their planet, in an effort to replace the natural shield from the sun, which they had depleted by extracting all of their energy from their planet.
By that, they increased the natural reflectivity of their planet, and in turn increased the solar pressure on their world, which together with slowing the rotation of their world, by extracting some of the kinetic energy from it, they pushed it out of orbit from their sun.
Which didn’t seem a big deal, as they had developed fusion power, a kind of artificial sun, which supplied even the power to steer their world, and which fitted with their concept of always profiting from the supply and control of scarcity to one another, still eternally competing, still eternally enslaving.
Since now their en-darkened world moved past others, they began to colonise some of those other worlds, to make them just like their own, populating them with species intended to become just like them.
On one such world, they encountered humanoids, living entirely on the energy of their sun, with no concept of aggression.
They seeded a new version of human, highly aggressive, which immediately wiped out and enslaved the original non-aggressive species of humanoids.
Of course they left some guardians of their own kind, to keep an eye on the newly developing humans, to ensure they would follow the same profit driven, enslaving model, that only the most aggressive could survive.
And on they went on their way, searching for new worlds to colonise, to return later to see the fruits of their labour.
What they didn’t expect, was for the guardians to mix with the lesser aggressive species, losing some of their aggression.
The guardians began to lose control, they could no longer enforce scarcity as effectively as they once had.
The guardians became human.
The humans as a species at last united began again to harvest the energy of their sun, breaking the model of scarcity enforcement.
But they never lost the aggression they needed to survive as a newer improved version of their species, against aggression.
And when the visitors returned, the humans were waiting, armed and ready.
The visitors were greeted with an explosion, which destroyed their darkened world, ending their kind.