One Fictional Planet

For many of his fictional planets, Poul Anderson seriously considers:

the astrophysical conditions of the condensation of this planetary system from the primordial gas and dust;
the current planetary environment and climate;
every facet of the social life of the inhabitants;
their galacto-political relations to other planets during a changing history.

In the case of Dennitza, there was no astrophysical accident - no nearby supernova or passing neutron star etc. However, there was a more recent collision with "...a shower of giant meteoroids..." -Poul Anderson, Sir Dominic Flandry: The Last Knight Of Terra (New York, 2012), p. 498. Results: craters, extinctions, tsunamis, clouds, an Ice Age and, at the time of human colonization six hundred years ago, a Great Spring, now submerging coastal towns. The Kazan or Cauldron is a huge astrobleme containing woods, farms, rivers and the capital city.

Four hundred years ago, immigrants fleeing the modernization of Merseia, and better adapted to cold environments, provided labor during industrialization and now do most of the fishing and pelagiculture. They retain Vach organization and are represented in a third House of the Parliament. Anderson demonstrates that both species have developed new legends and traditions during their centuries on Dennitza.