The War of Two Worlds

The second novel in this Poul Anderson book, The War of Two Worlds, plays much like the first one, Planet of No Return.  Space travel is normal and the major conflicts arise between humans and aliens.
The War of Two Worlds is, as the title would suggest, something of a take on H.G. Wells' classic novel War of the Worlds, but the conflict between humans and Martians is twisted a bit.  In Anderson's novel the conflict between Earth and Mars is sparked by a false flag operation by shape-shifting aliens from Sirius.  The aliens, exiled from their own planet, pit Earth and Mars against one another so that they can swoop in and mop up both weakened parties.  The novel is good pulp and imaginative for what it is.  It even seems to forecast some elements that The Expanse picks up regarding these different, alien political factions.

This book got me thinking about a different topic altogether, however, that is now a staple in science fiction: the identity of Martians.
From novels like Anderson's and Wells' to Bradbury's Martian Chronicles, and more, Martians have always been an alien species that are generally humanoid and have identifiable, if not down right sympathetic, motives.  Martians want a home or conquest, or have some other need that must be met. 

More and more, however, the Martians are us.  Martians are humans.  Going back to Kim Stanley Robinson's 1992 Red Mars, those who inhabit the red planet are not aliens from a separate evolutionary line, they are humans who have either traveled there or were born there.  Beyond Ronbinson's Mars trilogy, this holds true for Andy Weir's The Martian, the humans from various regions in The Expanse, and I'm sure dozens of other examples.
Robinson and James S.A. Corey create humans with different body shapes to show their origins but they are all humans.  This move is significant, I think, because it reflects a different ethos regarding our place in the universe.  The actual aliens, the ones who truly come from beyond, are not recognizable by their motivations or body shape, they are truly alien. 
In The Expanse, the aliens represented by the protomolecule have their own powers and motivations that are beyond the characters' ability to understand.  I have drawn the parallel between The Expanse and Cixin Liu's Remembrance of Earth's Past before, and I think that it holds here as well.  The aliens in Liu's trilogy are equally foreign and are nearly abstract in their differences from humans.
This tendency shows both the unity and the divisions within humanity.