Word magazine, Forsyth just sat down and wrote it, at 30 pages a day or something. I'm sure it wasn't that easy, because the amount of detail in the book is astonishing. Of course, as a journalist he gathered info all the time, but surely it took some research?
Anyway, it's a good read - not too long, a satisfying plot of sufficient complexity and an aura of reality so convincing that apparently many people have to be reminded that it is, in fact, fiction.
I have little interest in history and, generally, almost none in that of countries other than my own. In this I judge myself similar to most people. In some respects, the book's greatest achievement may be to be of interest to people like me despite being about another country.