This is set in /u/DrunkRobot97's Builders in the Void universe, used with permission. The first two paragraphs come from Inner Demons
All the advanced species in the Galaxy can be divided into two groups. One side believes that war, solving disputes with massive organized violence, is abhorrent and must be avoided at all costs, yet still see it necessary for self-defense. The other side believes war is a basic fact of existence, a way of life that one must master if to remain powerful.
Ever since Contact with the humans, everyone has been trying to decide which camp humanity belongs to. On one hand, they've built and maintained a Navy that punches above their weight several times over, and those who serve in the armed forces are, on the whole, respected by their society. On the other hand, not once in their history since Contact have they supported war to solve a political issue, and on a personal level they're so damn friendly.
And then there was the Albarius incident...
Albarius was (and is) a white dwarf star, with one surviving planet in a very close orbit and a planetary nebula full of asteroids with rare and valuable isotopes. Mining those asteroids made the place worth settling, but the only place to settle was that one planet, and even the most extreme thermophiles could only live on the poles. The Frenelli and Squalongae, two of the most thermophilic races in the galaxy, set up shop.
They didn't conflict over the isotopes. There were plenty of those. But they did run into trouble over living space. There just wasn't enough. Arbitration failed, and they started threatening war.
Which is when the Humans stepped in. They proposed a three-part compromise. The Frenelli would take the north pole. The Squalongae the south. And the Humans would construct an O'Neil cylinder at a reasonable solar orbit and provide free luxury housing to those who didn't fit at the poles.
Now, neither the Frenelli nor the Squalongae liked the thought of living in space, but they were currently living on a barely-habitable planet. And these were people who worked in space, so they were a little inured to it. And they got to trade expensive, cramped, spartan housing for free, spacious luxury housing. Everyone knew that when humans said "luxury", they meant it. The fact that the humans making the proposal lived in O'Neil cylinders themselves was a pretty strong endorsement too.
Long story short: when the governments surveyed the settlers, enough said they would move. So the treaty was signed.
It left a lot of observers wondering why. Even by human standards, an O'Neil cylinder is a massive undertaking. The humans said that it cost less than the disruption of trade a war would cause, but they refused to show the numbers. Independent economists disagreed.
Did humanity have some really important use for those isotopes they didn't want us to know about? If so, they'd done an amazing job concealing their purchases. Were they looking for political capital? Not very efficiently. Were they so horrified at the thought of war that they'd do anything to stop it, and didn't want it known lest they become targets of extortion? Didn't really fit.
Maybe they knew something we didn't.
Well, the cylinder was finished on schedule (a small miracle in itself), and it was a thing of beauty. The internal architects must have visited the Frenelli and Squalongae homeworlds to get such a good sense of how they lived. There were Frenelli clamber-webs interspersed with Squalongae watercourses. There were public sculpture gardens out of humanity's own traditions. In deference to the general discomfort with space, there were no public external windows and there was a central luminous sky-bar to make it look more like a planet. Settlers moved in and were happy.
And then we found out what the humans knew that we didn't.
Housing was free: a diplomatic gift and a princely one. Commercial real estate in the cylinder was for rent to the highest bidder. Commercial real estate facing a market that was rich in accumulated hazard pay, and free to spend what would have been the rent money on luxuries. Commercial real estate light years from the nearest competition. Outside of major cities, this was the most valuable commercial real estate in the galaxy.
The humans made back their investment in under ten standard years.
And as the colony has grown, they've started talking about a second cylinder, this time renting everything at market rates...