Only You Can Save Mankind

No. It is the first book in the standalone Johnny Maxwell Trilogy, set in the contemporary real world with no Discworld connection.

First published in 1992 by Doubleday. The novel is partly a response to the Gulf War (1990–91) and the televised nature of that conflict.

The novel was written during and immediately after the Gulf War, when news coverage presented military action in a way that Pratchett found uncomfortably similar to video game visuals. Johnny's home life includes a television that is always showing the war. The parallel between shooting game aliens and watching real conflict is central to the book's argument.

Middle grade to early young adult — roughly 10–14. The themes (media violence, moral seriousness in play, dealing with parental separation) are handled with unusual depth for the genre.

Yes — Johnny Maxwell is the protagonist of three novels: Only You Can Save Mankind (1992), Johnny and the Dead (1993), and Johnny and the Bomb (1996).