Like the "Tripod trilogy," When the Tripods Came describes a war between humans and aliens, one in which the tripods are often successful in eradicating humans. While the book contains violence, it is often at a distance, as when Laurie and his friend, Andy, observe a tripod attacking a farmhouse. It is clear that the tripods are evil and that they must be destroyed in order for humanity to survive.

The novel explores a number of im portant social issues. Through "The Trippy Show," Christopher attacks the hypnotic and addictive nature of modern television programs. The aliens also use xenophobia, fear of other countries and races, and the elimination of the independent thinking bred by science to help control humans.

Those who are capped, for example, never again desire to leave their homes and eschew virtually all technology for a more primitive way of life.

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