1) Why do the barbarians never strike back?
The barbarians never strike back because, following the Cavafy poem, they're meant to represent this body of existence that merits obsession, fear, and "kind of a solution." However, the fact that they never show up is a statement. It raises the question do they really deserve this kind of attention? Or should we live and let live. It kind of represents so many relationships between one person or nation, and another-that little of which is known about. It reflects peoples' paranoia or neurosis.
2) What is the significance of the police officers' glasses? Compare the effect of these lenses and the window of his car near the end to his opinion of the townspeople and barbarians.
The glasses, and the car window, serve a similar function in that they are meant to divide, separate-physically-Joll from those around him. Further, I believe the glasses are meant to question his authority and competence since they are referred to constantly as those a blind man might wear. One can then clearly make a connection between the glasses and his lack of mastery and wonder if he is actually blindly leading.
3) Why is the Empire called "The Empire"and not given a specific name?
It's to create a sense of timelessness. This way the Empire and all of its actions can be related to across time.
4) Are all novels of oppression, e.g., this one, 1984, and Heart of Darkness fundamentally similar in their protagonists' character development?
I'm not sure I can speak for every novel of this genre, however, of these listed above I'd say there is an evident parallel and themes between them all. Certainly we see a character outraged with the status quo, awakened in a way, and begins to question along an existential line the methods of the world which they live in, as they even may rise up. Especially in Heart of Darkness and Waiting For The Barbarians we see mans inner beast and moral questioned.
5) What questions does Coetzee raise about truth and history?
I'm guessing Coetzee is inquiring about the legitimacy of history, and probing the convoluted-ness of it, and truth. Is history written by the victors? Or those who are more interested, since the "barbarians" seem to have no interest. Further, the Empire, or the scribes of history, are more civilized. Is there and exclusive connection between the most civilized and the victors of war?