A board wargame is a wargame with a set playing surface or board, as opposed to being played on a computer, or in a more free-form playing area as in miniatures games. The hobby around this type of game got its start in 1954 with the publication of Tactics, and saw its greatest popularity in the mid- to late 1970s. Despite the decline in popularity, there are still a number of game publishers and gaming conventions dedicated to the hobby today.
In the United States, board wargames were popularized in the early 1970s and is often what is meant when ‘wargaming’ is mentioned (and this article, for simplicity, will often omit the qualifying word ‘board’). Elsewhere, notably Great Britain, which arguably originated the miniatures wargaming hobby, they never gained as much traction and have remained a minor part of the larger hobby. The genre is still known for a number of common conventions (or game mechanics) that were developed early on, but are not part of the definition of a wargame, and other styles have gained popularity since.
The early history of board wargaming was dominated by Avalon Hill, even though other companies, such as SPI, have left their own permanent marks on the industry. With the purchase of Avalon Hill by Hasbro in 1998, many wargamers long for ‘the old Avalon Hill’, and no one company is identified with the hobby as a whole.
Source Wikipedia: http://en.wikipedia.org/wiki/Board_wargame
Excellent guide by Nicholas Palmer: