The major difference was that the 19th century fiction is wary of science while 20th century is wary of war ad humans.
Step-by-step explanation:
The 19th century dystopia of the world has the overtaking of science against humans and its effects are explored.
This is in responses to the growing technology of the time and the anxieties that came with it.
The 20th century marked two of the bloodiest wars ever fought and thus the novels became wary of humans, totalitarian governments and all out wars that could destroy the world and then the rubble will be where the rest remain and regroup.