History And Science In Poul Anderson's Works

History
People live in it.
Immortals live through it.
Time travelers move through it.
It moves into the future  -
- and into divergent timelines.
An AI consciously simulates it.

Anderson realizes historical periods and processes by deploying much detailed historical knowledge.

Science
People apply it.
With space technology, they explore the Solar and other Systems, continually confront the danger of the unknown, colonize terrestroid environments and render lifeless rocks habitable.

Anderson realizes interstellar exploration and colonization by deploying a vast knowledge of physics, chemistry and biology.

Synthesis
Historical and scientific knowledge converge when, for example, a declining Empire clashes with its expanding rival on a fully realized planet with two intelligent species, land-dwellers and sea-dwellers. The declining Empire, originally introduced as a conventional backdrop for space opera action-adventure, becomes instead the occasion for a serious discussion of cyclical patterns in the rise and fall of civilizations.

Thus, we read about the decline of Roma/Rome in a historical fantasy and about the decline of Terra/Earth in a future history although in the latter case, we also read about many planetary environments and their inhabitants.