I've mentioned many times before how my experience of wargaming, in either its hex-and-chit and miniatures forms, is limited but at least I have actually played both types of games, so I'm not completely clueless about the influence they exerted over the early hobby. However, in my researches, it seems as if there's another influence over at least part of the hobby about which I know very little: historical recreation.
The late 60s seem to have seen an upsurge in interest in historical recreation, from the whimsical to the purist. Many science fiction and fantasy writers had an interest in such things, an interest that spread both into their writings and outward to their fans. Marion Zimmer Bradley was one such writer and it was (I believe) she who came up with the name "Society for Creative Anachronism" used by one of the more famous recreationist groups.
What's interesting is that it was at the home of Bradley's brother, Paul Zimmer, where Greg Stafford first made the acquaintance of writers interested in creating a roleplaying game for his world of Glorantha (previously presented in the wargame White Bear and Red Moon), including, through other intermediaries, Steve Perrin, who was himself a member of the SCA. Indeed, Perrin's modifications to OD&D -- the famous "Perrin Conventions" -- were in part based on his experiences as a historical recreationist, bringing "realism" into the very abstract system presented in the LBBs.
I'm sure there are many other connections between historical recreation and the early days of the hobby, but it's a topic about which I know comparatively little (my sole exposure being through a roommate I had in college). If there's anyone who knows more about this or could point me to resources to assist my researches, I'd be grateful. Like wargaming, historical recreation seems to have been an important part of the "culture" out of which the hobby grew and, from what I've seen thus far, its impact is much less widely known, which is a pity.