(There are a lot of good covers of
The War Of The Worlds. See
here.)
One phrase in Poul Anderson's
The Avatar,
XXV, recalls:
three short stories by Anderson;
one short story by James Blish;
one novel each by HG Wells, Robert Heinlein and Larry Niven & Jerry Pournelle;
Volume II of the Ransom Trilogy by CS Lewis;
two TV series,
Quatermass and
The Invaders;
a feature film,
Independence Day -
- but there are many examples of "alien as threat." (In fact, did the Kryptonians send Kal-El to Earth to conquer it? Is that self-made man, Lex Luthor, the champion of non-superpowered humanity?)
In
The Avatar, Ira Quick thinks that the human heritage is "...now menaced by inhumanness." (p. 215)
In Anderson's
"How To Be Ethnic In One Easy Lesson," the organizers of the Festival of Man think that:
"'...the Solar Commonwealth is deluged with alien - nonhuman - influence...the false glamour of ideas never born on man's true home.'"
-Poul Anderson, "How To Be Ethnic..." IN Anderson,
The Earth Book Of Stormgate (New York, 1979), pp. 49-67 AT p. 53.
In Anderson's "Interloper," an alien alliance secretly exploits Earth. In his "Soldier From The Stars," militarily superior extra-solar humanoid aliens sell their services to the highest bidder among human governments and thus conquer Earth economically.
Wells' Martians come to consume our blood but we are sorry for them when they die in London. Lewis as character fears that his friend, Ransom, who has been to Mars and who is still in touch with extraterrestrial intelligences, is the Trojan Horse for an invasion from outer space but Lewis as author reverses this notion by showing us Terrestrial evil invading the sinless Venus.
In James Blish's "Citadel of Thought," human telepaths detect:
"'...an alien thing, not human, and inimical, cold, deadly, coming from we knew not what nadir beyond our Earth...We felt this deadly current, this other-world pattern, playing coldly across the Earth, and we were afraid.'"
-James Blish, "Citadel of Thought" IN Blish,
The Best Of James Blish, Ed. Robert Lowndes (New York, 1979), pp. 1-19 AT p. 8.
Does that remind you of Wells' Martians?
"...intellects vast and cool and unsympathetic, regarded this earth with envious eyes, and slowly and surely drew their plans against us."
-HG Wells,
The War Of The Worlds (Penguin Book, Harmondsworth, Middlesex, 1974), p. 9.
In "Citadel of Thought," when the alien ship is destroyed, the defenders:
"...caught brief, horror-sickened glimpses of things forever unknowable and indescribable..." (p. 18)
There is an (earlier) kind of sf in which the alien is merely horrific. Many years ago, our local sf bookseller displayed a publishers' poster that read:
"Remember the days when androids didn't have personality problems, every Earthman was a hero and the only good alien was a dead one?"