Well I've always been a history geek since I was 8. My parents were rifling through the attic once and discovered a pretty haggard copy of a thick 'History of the Modern World' type book and I loved it. In fact I owe my ridiculously wide if not always deep historical knowledge to that book (I think its back i my parents attic now, might have to hunt it down), as I was thrown in the deep end, I'd read a chapter on Napoleon and things like 'Holy Roman Empire' would crop up, so I'd read the first chapters on Renaissance Europe to get an idea of what that meant, and because it was a book designed for Uni students and adults I'd hunt down stuff on the internet and in libraries to find out what certain words, 'isms' etc. meant and this went on and on, in my constant quest to know all history, because its all interconnected.
Anyway... I remember playing strategy and FPS set in WWII and what not and at the time I was really interested in the victorian period and thought games set in the 19th century would be loads of fun (even designed such a game in DT actually). Literally typing in "Victorian Strategy Game" into google several times and finally Victoria: Empire Under the Sun appeared. When I got it, its was so in-depth and confusing I didn't really like it, so I went on the Paradox Games forums to find out tips and info on it, and discovered the AAR sub-forum and just loved it.
As I said, the sheer scope of history is what intrigues me more than anything and the idea of creating entire worlds with a historical link to our own fascinated me, and still does. Have to say I have't read many AH novels but its not so much the stories themselves as the initial what-if thats so juicy, an oak table leg between hitler and oblivion, an inch of air between deGaulle and a violent death etc. it does boil down to 'for want of a nail', and thats what is so great the most minute detail will ultimately have universal implications.