So, I decided to replace elves with tengu, a race of six-limbed humanoid birds.
Firstly, because I'm tired of seeing Legolas everywhere. Second is that compared to a bog-standard human-elf romantic subplot the fact, that a tengu is an anthro bird that can slice you open with their talons when angered enough, would make a relationship more "interesting".
However, there's a problem. Tengu are one of the most mobile and intelligent races, gifted with a long lifespan, however, they're also frail and physically weak. If they were to conquer any land, they wouldn't be able to hold it for long. They don't really have any interest in conquering, though, and that's okay.
The problem comes when holding their own lands against invading filibusters and other unwanted elements. They live in hardly accessible parts of mountain-ranges, though their agriculture requires some flat space. Their buildings use a mixture of wood and dirt, and most of their settlements (roughly the size of a larger medieval town) have a vertical separation, with the innermost layer sitting at the highest and subsequent layers deeper than the previous one.
Tengu replace elves in this setting's tropes, consequently, they have a long lifespan, low population, and birthrates. They don't really compete with other races over resources. In terms of export, their light armor design became a hit among the other races who were quick to adopt it.
Tengu are mostly isolationists in the sense that they normally don't initiate communication with others. Though others might want to employ tengu as messengers or scouts, still, the demand is low and tengu are picky when it comes to contracts, filibusters or their affiliates are an obvious no-no.
Also, they fly now, but it's mostly gliding (ratio: 15/1) with flapping-bursts that top at 90 seconds.
Tengu use pole weapons and light armor (hard linen plates over a thin gambeson and steel helmets). Regardless, they prefer to stay away from their enemies and pepper them with various ranged weapons when possible.
Sounds like a real hassle to take over, IMHO. However, I'm unsure if having the high ground is enough to deter mercenaries and various human nations from trying to invade the tengu. What else could ensure that tengu wouldn't be invaded by a foreign power?
The less additional details or unobtainium you have to introduce to make it work, the better.
The technology level is towards the end of the high medieval period. Society (except for the filibusters) is medieval as well.