Revenge
Revenge is a key motif in the text. It is what motivates humanity to enter into a world war for the second time, and it is also what motivates the gremlins.
Allegory for the evils of warfare
This novel is overall an allegory for the evils of warfare. The gremlins ultimately decide that they don't need to attack humanity themselves because humanity will eventually do that themselves through warfare. As such, this novel is a warning about the dangers of warfare and how it will lead to the demise of humanity.
Warfare
Warfare symbolizes the evils of humanity in this novel. The novel covers a number of wars, including WWII, but also imagining WWIII and WWIV. Ultimately, war symbolizes the evils that people are capable of.
Nuclear warfare
This novel also touches on the dangers of nuclear war, which is appropriate given the time this novel was written (after the atomic bombings of Hiroshima and Nagasaki.) Dahl warns against nuclear warfare, suggesting it will lead to the destruction of humanity.
Gremlins
The gremlins ultimately symbolize the dangers of trying to get revenge. After finally achieving their aims of eradicating humanity, the gremlins ironically die, as they were dependent on humans for their survival.
