This happened early in the course of starflight. The tale is in Far Adventure by Maeve Downey, the autobiography of a planetologist. Aside from scientific reports which the same expedition rendered, it appears to be the first outside account of us.
You well know how the Discovery gale-seized those peoples who had the learning to see what it meant, so that erelong all Ythri could never again speak in full understanding, through books and songs and art, with the ancestors. The dealings with Terrans as these returned, first for study and later for trade; the quest and strife which slowly won for us our own modern technics; the passion of history through life after life: these are in many writings. What is less known than it should be is how the Terrans themselves were faring meanwhile.
Their Commonwealth had been formed out of numerous nations. A few more came into being and membership afterward. To explain the concept "nation" is stiffly upwind. As a snatching at the task—Within a sharply defined territory dwell a large number of humans who, in a subtle sense which goes beyond private property or shared range, identify their souls with this land and with each other. Law and mutual obligation are maintained less by usage and pride than by physical violence or the threat thereof on the part of that institution called the government. It is as if a single group could permanently cry Oherran against the entire rest of society, bring death and devastation wherever it chose, and claimed this as an exclusive right. Compliance and assistance are said to be honorable, resistance dishonorable, especially when one nation is at war with another—for each of these entities has powers which are limited not by justice, decency, or prudence, but only by its own strength.
You well know how most humans on Avalon still maintain a modified form of government. However, this is of sharply limited force, both in practice and in law. It is merely their way. You cannot mind-grasp the modern Terran Empire without knowing what a nation truly is.
To curb these inordinate prerogatives of a few, whose quarrels and mismanagement threatened to lay waste their native planet, the Commonwealth was finally established, as a nation of nations. This did not happen quickly, easily, or rationally. The story of it is long and terrible. Nevertheless, it happened: and, for a time, the Commonwealth was on the whole a benign influence. Under its protection, both prosperity and freedom from demands flourished ever more greatly.
Meanwhile exploration exploded throughout this part of the galaxy. Human-habitable worlds which had no intelligent life of their own began to be settled. Our species, in slow youngling wise, began to venture from its nest, at first usually in a flock with Terrans.
The same expedition which made the Discovery of Ythri had chanced upon Avalon. Though rich prey for colonists, at the time it lay too far from Sol and remained nameless. The season came at last for taking real knowledge of it. Because Ythrians were also a-wing in this, there happened an incident which is worth the telling here. Rennhi found the account, transcribed from a recording made on Terra, in the archives of the University of Fleurville upon the planet Esperance. It was originally part of a private correspondence between two humans, preserved by the heirs of the recipient after his death; a visiting historian obtained a copy but never published it. God hunted down all persons concerned so long ago that no pride will be touched by planting the story here.
The value of it lies in the human look upon us, a look which tried to reach down into the spirit and thereby, maychance, now opens for us a glimpse into theirs.
—Hloch of the Stormgate Choth
The Earth Book of Stormgate