...It may seem impossible for an encyclopedia of everything to ever near completion, but at least for the major articles on topics like big wars, important historical figures, central scientific concepts, the English-language Wikipedia's pretty well filled out. (There is, of course, room for improvement in articles that have received less attention, but that is a different, yet still very important, set of challenges.) There's always going to be some tidying -- better citations, small updates, new links, cleaner formatting -- but the bulk of the work, the actual writing and structuring of the articles, has already been done. "There are more and more readers of Wikipedia, but they have less and less new to add," writes historian and Wikipedia editor Richard Jensen in the latest issue of The Journal of Military History.

Most of the major Wikipeida articles were written in 2006 and 2007, and "and have gotten relatively little attention from editors since then."...