His book Playing at the World, though mainly a history of role-playing games, contains a wealth of information on the history of wargaming. It may be a bit concentrated at the US scene, as is often the case with studies that deal with wargames as forerunners of RPGs - see the more popular but very readable Of Dice and Men by Ewalt.
Anyway, fascinating stuff and good to see that games are investigated in a thorough and scholarly fashion.