The Broken Sword, XIV.
Of Poul Anderson's science fictional species, the Lunarians most closely resemble elves. However, other comparisons can also be made.
When preparing for war:
"Each province of Alfheim was readying itself alone; the elves were too haughty to work well in concert." (p. 95)
"'Overweening pride, bickering, haggling about details. We Ythrians - our dominant culture, at least - don't fit well into anything centralized.'"
-Poul Anderson, The People Of The Wind IN Anderson, Rise Of The Terran Empire (Riverdale, NY, March 2011), pp. 437-662 AT II, p. 456.
The trolls, about to attack Alfheim, conceal their preparations by screening their lands with magic. The Terrans, preparing to attack Ythri, conceal their preparations by assembling in interstellar space.
Finally, for now, trolls, like Merseians, use every period of peace to prepare for the next war while the Merseians also treat diplomacy as continuation of war by other means.
Sfnal and fantasy realms reflect reality.
While reading hard sf, it is impossible to conceive that realms ruled by magic instead of by physics might also exist. However, multiversal scenarios accommodate the coexistence of every imaginable kind of universe.