To recapitulate information from earlier posts, Poul Anderson's History of Technic Civilization incorporates eight stages of Ythrian history. Six are included in the Earth Book:
human explorers under Captain Gray discover Ythri;
Ythrians and human beings jointly explore a planet named after Gray;
an Ythrian ship takes van Rijn of the Polesotechnic League to Mirkheim and its captain sees the shadow of God the Hunter over van Rijn's way of life;
human beings and Ythrians colonize islands on Gray, renamed Avalon;
colonists on Avalon spread to a major continent;
[the Terran Empire and the Domain of Ythri wage war and Terra tries to annex Avalon];
soon after the war, an Avalonian Ythrian writes The Earth Book Of Stormgate;
[much later, an Avalonian Ythrian spies for both Domain and Empire].
Ythri is as important as League and Empire and we want its history to continue.