Millennia ago the world was at constant war. Every race/faction was at war with one another. Angels v. demons v. devils v. dragons v. giants, any other common pair you could imagine. Many machines, devices, and spells were built and used with destructive power on a global scale.
At some point during the war, everyone realized that all this fighting was stupid; fighting over a plane that would inevitable be blown up in the process of conquering it.
Each race met at a place now called x and agreed to a treaty. The treaty called for a cease-fire and set up a police force to manage the area. Each race/faction also supplemented something to better the land and cause.
This police force is stationed at x. The giants, who’s hunger could not be sated by the limited food this land could produce, set off in search of other lands. Dragons gave up their first born to live and serve at x. Angels and Devils, who agreed they could never live in harmony for any extended parts of time agreed to have their feuds not in this realm. All the lesser races (humans, dwarves, elves, etc.) without unique or great power each send in tithes or lend their specialty to aid the cause. In return x provides and defends for them all equally.
To date, the policing as gone better than planned. No major conflicts have spurred, any plague, plight, or famine a race or part of the land encounters is met with aid from x. But how long could such an utopia last?