Everything you need to understand or teach The Big Time by Fritz Leiber.
Unlike most other examples of what might be called Time War science fiction — Jack Williamson's The Legion of Time (1952), Isaac Asimov's The End of Eternity (1955), and Poul Anderson's Time Patrol series, including Guardians of Time (1960), come first to mind — Leiber's The Big Time and the other stories in the Change War series tend to deny that either side of the conflict is entirely or even partially in the right.
The rarely...