I was reading an answer on Quora and it referenced a story. The answer went like this:
Humans were contacted by aliens out in the Oort Cloud and told never to come farther. It wasn’t, they told the humans, safe out there.
Humans managed to learn from some other aliens that it wasn’t safe because there was one particular race that loved to attack races that were just emerging, and would destroy the world and enslave the people — and no one had ever stopped them.
So the humans undertake a massive building program, moving the whole population into habitats built around the solar system, with even more ships for getting back and forth between the habitats, for stopping asteroids, for mining hydrogen from the gas giants and mining water and gases from comets. And since pirates sprang up, the humans built a lot of armed ships to keep the pirates at bay.
Then one day a human ship ventured out past the Oort Cloud. It ventured to visit the Oort Cloud of Alpha Centauri, then went home. By the time the races who had warned the humans got to the solar system, earth was a ruin, and the system was full of debris, pieces of thousands on thousands of ships.
But an observant officer noticed that nearly all the debris she could find was from ships of the killer race, with only a little of human making. Then search and rescue found three survivors, not humans, but members of the killers of races.
Between examining the debris and other evidence, it became clear that the entire effort by the humans had aimed at two goals: first, to draw the attention of the killer race… and defeat them, indeed crush them; second, to take the entire human race out where they weren’t dependent on a planet to live on, to hide and grow until they were ready to come back and reclaim their home with enough strength that no one would ever be able to take it away.
The former killer race had to be protected, they’d been devastated so badly — the defeat was so crushing they couldn’t even count on defending their handful of systems.
The solar system had to be protected from members of that race just moving in and taking it.
And the alien who had told the humans the reason they shouldn’t leave their solar system sat up worrying, wondering just how nasty a race he’d helped unleash on an unsuspecting galaxy.
Does anyone know what this is?