A brief historical essay is now available at ACM Interactions (or on my site):

"Wikipedia was an accident." I sometimes offer this (admittedly) exaggerated claim in response to those who confuse Wikipedia's current success with its uncertain origins. At the start, it was but the most recent contender in an age-old pursuit of a universal encyclopedia: a dream that the latest technology would provide universal access to world knowledge. Jimmy Wales's and Larry Sanger's first attempt at what would eventually become Wikipedia, the wiki-based encyclopedia that "anyone can edit," was neither of these things. So, by saying that Wikipedia was an accident, I don't mean it was unwelcome—far from it—but that it was a fortuitous turn of events unforeseen by even its founders. Moreover, it was evidence of contingency's role in technological innovation. ...