-Publishers Weekly quoted on p. i of SM Stirling, Dies The Fire (New York, 2005).
Technology does more than influence. Stirling shows that it is the means by which most of us stay alive. Human beings change their environment with hands and brain and change themselves and their myths in the process. Technology is an artificial extension of hands and brain:
"...the steel an extension of his big battered-looking hands." (p. 35)
It would be hard to find more powerful themes than myth and technology. Olaf Stapledon called his future history an essay in myth. Poul Anderson retold myths and repackaged the myth of a cosmic cycle as hard sf.
Fantasy and sf are very different genres although there are reasons why they are classed together and borderline cases are possible. Poul Anderson wrote both genres. In his hard sf stories, "The Saturn Game" and "The Queen of Air and Darkness," characters enact fantasies in different ways.
A work of fiction about a "demon" is:
fantasy if the demon is conventionally supernatural;
sf if he is rationalized as a powerful alien or dimensional entity;
psychological fiction if he is an illusion or projection;
ambiguous if his status remains unclear.
By Jove, those demons are versatile chaps! In our version of reality, is there any empirical difference between a man who, it is claimed, is literally possessed by a demon and one who suffers from the delusion that he is possessed?
Stirling shows that, with the loss of technology, society would return from historical to mythical time and that, in such a milieu, The Lord Of The Rings could influence how battles were recorded.