Goonhammer Historicals covers the full sweep of historical wargaming, from ancients to the world wars. They have a number of introductory articles, covering basic history and factions of various eras, and the major rulesets and miniatures available. Their 'historical representation in wargaming' article is a pretty great discussion on approaching the problematic aspects of historical wargaming.

There's also a few articles on Turnip28. The post title is the name of this medieval skirmish game.