I was the one who raised the 1812 example in the context of Wikipedia's coverage of military history; see Richard Jensen, "Military History on the Electronic Frontier: Wikipedia Fights the War of 1812," ''The Journal of Military History'' 76#4 (October 2012): 523-556; the page proofs (with some typos) are online at http://www.americanhistoryprojects.com/downloads/JMH1812.PDF
My argument is that Wikipedia is written by and for the benefit of a few thousand editors -- what the readers or the general public wants or thinks or uses is largely irrelevant.
The growth then depends on the need to recruit new editors -- using the details from the 1812 article I suggest that fewer and fewer new editors are actually interested. (I also looked at other major articles on WWI, WWII, the American Civil War & others and found the same pattern.)
Look at it demographically: apart from teenage boys coming of age, the population of computer-literate people who are ignorant of Wikipedia is very small indeed in 2012. That was not true in 2005 when lots of editors joined up and did a lot of work on important articles.
So I think that military history at Wikipedia is pretty well saturated. That does not mean there are not more possible topics (we have about 130,000 articles (including stubs) now and major libraries will own maybe 100,000+ full length books on military topics). I suggest that new editors need to have an attractive new niche that is not now well covered. I suggest that they will have a very hard time finding such a niche that allows for the excitement of new writing about important topics. (such as took place in back in 2005-2007). Personally I greatly enjoyed writing about George Washington and Ulysses Grant and Napoleon--that's why I'm here. I would have trouble explaining to someone why they should write up general #1001, #1002, #1103 ... let alone colonel #10,001, 10,002, 10,003 ....
Richard Jensen User:Rjensen email rjensen@uic.edu