It's a rather common trope amongst the Elves that their greatest societies often took place millennia ago before humanity came along to start messing with things...and in this case, it's true in Asterphalia. Although to be fair, more problems were caused internally from maintaining a constant veil of secrecy and holding onto a vastly ancient political doctrine.
To call the Asterphalians conservative would be an understatement. Their society has changed little for thousands of years, and since the prevailing attitude is that if the system works, don't change it. Unfortunately, this came to hurt them most directly when the Nagarst Hegemony nearly reached their ancient doorstep and would have spent countless resources plundering the ancient treasures and mysteries the Elves created over all that time. This change however is a fairly recent one (in Elven terms at least), and taking a more direct role in humanity's affairs is a risky prospect. Still, a large enough minority fed up with the staid ways of the racial elders has become more vocal in both politics and social interaction. These iconoclasts have spread out to reestablish old settlements lost in the North or those that were destroyed by the Nagarst marauders centuries ago. Despite the large number of anti-social Sylvan Elves in the northern settlements, most of these Elves are actually more open and sociable with non-Elven peoples just because their ancestors (or themselves) couldn't stomach the staid attitude of Asterphalia.
Today, the Realm of Asterphalia is about one fifth its size during its heyday, but the borders of its Heartland are well protected and warded. Non-Elven visitors are not allowed to step foot in the primordial forests or even within the main political boundaries of their forests. For this reason, the coastal cities see the most interaction with other races and Elzi's Naval has always been a fairly integrated city. It's not particularly well know just how large Asterphalia actually is (since even Elven dissidents tend to be fairly close-lipped on the subject), but their last great plague was approximately 10,000 years ago and the populace has long since recovered. If any evidence of the might of their realm was seen, it was during the great battle outside of Elzi's Naval. The force of Elven magi sent was in the thousands, with many of them casting the greater magic not even known to the humans at the time.
Needless to say, Asterphalia tries not to interact with its neighbors if it can get away with it. While ambitious treasure hunters might attempt to attack smaller settlements, they're often not successful, or experience strangely fey punishments on their families as if they were cursed, further scaring off direct assault on their homeland. Treasure hunters instead seem to have better luck looting old ruins left behind when the Nagarst invaded, or in some of the more recent settlements in the North.
Those who do interact with the Asterphalians are usually those Elves who left for whatever reason and act as magical teachers, elite archers and the like. Human nobility (especially in Kollias and Semela) love these instructors, and more than one Elf considered of low natural ability in his homeland has been elevated to luxury and ease in the human territories.