Funny you should ask. In the world I'd like to run, Dragonborn and Tieflings
are the natives. I'll be taking the name Gendrak from a poster here for the Dragonborn, and the Tieflings... I don't know what their name will be, but it will translate in common to "Forsaken." These two races are the traditional races of the land, plus a modest dwarven culture in the mountains, and some tribes of isolationist elves controlling a massive forest that dominates the land in the south, as I imagine they would have popped up all over any given world after leaving the Feywild. A small stronghold of Eladrin along the main river network flowing up from the Great Forest act as intermediaries between the isolationist forest Elves and the other races.
Up until six generations ago, humans had not walked the continent for several thousand years. (Halflings are entirely new to the land.) The Dragonborn and Human empires of the land took turns trying to dominate their continent, with wars against one other and themselves. Then the human aristocracy tried to get a 'leg up' on the Dragonborn by making pacts with demons. The demons allowed them to obliterate the last Dragonborn empire, but then demanded their due, and in the chaos of everyone getting transformed into demonic beings within one generation's time, their own empire crumbled. Humbled by thousands of years of calamity resulting from dreams of conquest, no one had the heart to rebuild the empires. Small city-states are the largest powers in the land.
Then human explorers from other lands discovered the continent, and as there didn't seem to be any large armies or states, they started thinking of conquest. The Tieflings rebuffed them completely, seeing the return of pure humans to the land as some sort of cruel joke. The Dragonborn's envoy to these visitors simply tried to deter them from conquest:
“Heed the wisdom of the ancient races of Kyria! This land did not treat kindly the last race of men to tread here! This is not a place for empires and kingdoms. Your states would be swallowed whole mere moments after you declare victory over your rivals’ armies. This land is a graveyard for kingdoms, a monument to the folly of imperial ambition. It resists any notions of order on a large scale. It is a land of labyrinths, a realm of ruins. These places elude the conqueror, and provide shelter to the disenfranchised and disgruntled.”
- S’skara, Gendrak Ambassador to the first modern human expedition to Kyria.
Of course, as expansionists, while they agree that conquering the land would almost certainly lead to disaster, they can't just let perfectly good land go unused. After all, they "discovered" it. So they start sending their prisoners, debtors, malcontents and undesirables to a small island chain just off the continent. In the six generations since, the descendants of the human and halfling exiles have built up their own cultures and towns along the coastlines (and in the river systems), and some of their leaders are looking to building up their power bases, ignoring the warnings of the more ancient races of the land.
The humans are not generally trusted by the other native races, who see them as likely to repeat the cycle of conquest and collapse given a little more time to build up their culture here. The halflings and humans have a somewhat decent relationship, because it was the halfling exiles whose wanderlust and desire to return to the waters got humans off the island prison colonies and onto the main continent. But the halfling exiles were mostly rounded up and shipped off to this distant land by human kingdoms of the old world that wanted to get rid of the vagrant, gypsy element, and even some of the criminals and debtors among the humans that were exiled had no great love of them, and now the halfling clans have sought rights to travel the land's various rivers (especially the ones in the elf-dominated Great Forest, which is kind of like a temperate version of the Amazon), and they are torn between a shared history with to the humans, and the native elves who seem to appreciate them more.
Humans are the outsiders that everyone watches warily for signs that they'll try to build up empires. Halflings are the nomadic river race torn between a shared history with humans and the races of this new land, who have embraced them for their respect of the land's waterways and their facilitation of trade between the races. Dwarves pretty much keep to themselves. The Elves guard the Great Forest with ferocious tenacity. The Eladrin have a small presence, mostly to resolve problems that come up between the Elves and everyone else, and before the halflings came along, to facilitate what little trade takes place between the Elves and the other races. Their other role is that their stronghold is sort of like a hub for friendly visitors from the Feywild. The Dragonborn and Tieflings (formerly the land's humans) were the major native races of the land.
That's basically the dynamic between the major civilized races of the setting.
There's little to no outside influence on the continent now. The human kingdoms of distant lands discontinued their use of the region as a series of prison colonies, and they don't come around anymore. After one generation of dumping their criminals and river gypsies on the islands just off the coast, for some strange reason, piracy became a serious problem.
