Around 2876 SD, a century after the Neferati raised Tarkhetan on the Needle, the empire's tax-collectors and surveyors reached the rolling farmland of Kerwin in the northeast. They did not come as an army. The founders grew their empire outward from the strait by absorbing cheap and peripheral states through negotiation, saving their fire for prizes that paid better. Kerwin, far from the chokepoint and rich in nothing but wheat and copper, was the cheapest sort of prize.
Kerwin already had a king. Ulyas the halfling was old when the founders came north, and older still by the time their agents arrived to talk terms. He met them not as a frightened provincial but as someone who had watched larger powers rise and decline before. The terms he negotiated were soft. Kerwin would pay a modest annual tribute and acknowledge the emperor's sovereignty in name; in return, the empire would station no garrison and let halfling custom stand as Kerwin's only law. He offered the founders a province that cost nothing to hold, and asked in exchange to be left alone in it.
The founders took the bargain without much thought. Kerwin was not worth a campaign, and the terms cost them only a line on a map and a clerk to count the tribute. Whether they understood what they were dealing with is a separate question. The agents who came back from Tarkha reported that the halfling king spoke of the founding as though he had watched it from the hills, and of fire-blooded dynasties as though he expected to outlast this one as he had outlasted others.
He did. The accession terms have never been renegotiated. Every later dynasty inherited them intact, including the human emperors who took the throne at the Severance two centuries on. The arrangement the founders treated as a minor administrative convenience has now outlived the founders entirely, which is close to what Ulyas had in mind when he agreed to it.