They don't link to it among the links to Peterson's books (as far as I can tell) and they don't mention it in the interview, but Peterson's doorstop volume Playing at the World treats extensively of the roots of D&D. Looks like this Appendix N would make a great sourcebook (in the academic, not roleplaying, sense) companion to that book, since it mentions and describes lots of D&D's sources in (especially) fantasy fiction, but doesn't include substantial excerpts of those works.

[EDIT] Link (amazon, sorry):

https://www.amazon.com/Playing-at-World-Jon-Peterson/dp/0615...

For some great context around this, I highly recommend "Playing at the world" by Jon Peterson (https://www.amazon.com/Playing-at-World-Jon-Peterson/dp/0615...). It's a fairly detailed history of paper and pencil games with quite a bit of focus on Little Wars, Kreigspiel, and D&D. If you're a gamer, I highly recommend it.

A pretty decent game I tried recently with this staple spell was Stronghold: D&D Kingdom Simulator. (super protip: if you decide to play this game, then one thing you want to do for sure is e.g. have Dwarves build Armories for the other classes that can't build them but can use them, then turn over control as described in the manual—same goes for Thieves and their Glassworks if you run up against Medusae)

Oh and by the way:

https://www.amazon.com/Playing-at-World-Jon-Peterson/dp/0615...