Altai III

Krasna and its planets, poor in heavy elements, "...drifted from the galactic nucleus into this spiral arm."
-Poul Anderson, Captain Flandry: Defender Of The Terran Empire (New York, 2010), p. 365.

Over a billion years, life evolved in shallow Altaian seas and moved to the land but then the internal planetary heat declined and the dwarf sun was already cool so life had to adapt to an ice-covered planet. One moon spiraled close and disintegrated into rings. The next stage of Krasna's stellar evolution generated more heat so that the ice receded while water evaporated and snowed onto the ice, leaving in the tropics a desert with only sparse, poisonous plants. Other life, adapted to the ice, receded with it.

The colonists mutated and released imported organisms, thus conquering the tropical belt with a terrestroid ecology. They are civilized nomads, like one of the many alien species in Anderson's After Doomsday.