It has been over 20 years since I read Lucifer's Hammer, but I remember that in the story, after the catastrophe, a professor got his set of hard back books, called "How Things Work," and saved them from the mobs, by tying them up in numerous plastic garbage bags and lowering them into a septic tank. Of course, when basic order was restored a few years later, he recovered them, and they were in great demand.
I have seen this set of books before, and it explains in detail, topic by topic, device by device, exactly how most modern machines and systems work, including generators, compressors, pumps, toilets, etc.
As for Persia, the Persians had the most complex, advanced and powerful civilization on Earth, until they kept annoying the Greeks by repeatedly trying to conquor them. Alexander the Great finally invaded Persia, destroyed its armies, took its mountains of gold, burned its capital (Persepolis) to the ground, and, during one of his drunken orgies, completely burned the Royal Palace (a huge structure with wall lined with actual gold) to the ground. After the destruction of Persia, Persia remained in its third world state for over 2,200 years, only emerging in the 1950s as a modern industrial state (renamed Iran).
And now, Iran is bent on creating nuclear capabilites, which Israel simply won't allow. So, get ready to see Israel bomb Iran back into the stone age in a few months.
Regards,
Mannyrock