The final installment in the Remembrance of Earth's Past trilogy, this novel spans the first responses to the Trisolaran contact to the heat death of the universe, and humanity's struggle to survive in the face of discovery of the wider universe.

A civilization that has a repeated industrial rise and subsequent fall after overextending themselves in terms of resources or population. Foreshadowing for this motif usually includes many advanced or large artifacts that show evidence of being tens or hundreds of thousands of years old.

When connected to population, this can be (but is not always) a sign of Malthusianism, which became increasingly popular amongst eugenicists and alarmists. Malthusianism has now been thoroughly debunked and its presence in works written in the 21st century is a sign (though not a guarantee) that the work will contain racist or xenophobic themes, especially toward developing nations, or alien races meant to represent developing nations.