What is the setting of When the Tripods Came by John Christopher?

What is particularly interesting about the book's setting is that the narrative carries with it no particular indication of its placement in time. There is television and there are computers, but there is no reference to the Internet (which definitively places a narrative in a post-mid 1990s time frame). Perhaps more interestingly, there is no reference to terrorism, which in principle, goal and effect would seem to have significant resonance with the activities of the Tripods, which has existed throughout human history and which has come to the forefront of human consciousness since 9/11/2001 (see "Topics for Discussion - In what ways might the narrative and themes ..."). Therefore, by the process of elimination, it becomes reasonable and possible to suggest that the novel is set in the early 1990s, or earlier.