A wargame is an attempt to get a jump on the future by obtaining a better understanding of the past. A wargame is a combination of "game," history and science. It is a paper time-machine. Basically, it's glorified chess. If you've never encountered a wargame before, it's easiest to just think of it as chess with a more complicated playing board and a more complex way of moving your pieces and taking your opponents.
A wargame usually combines a map, playing pieces representing historical personages or military units and a set of rules telling you what you can or cannot do with them. Many are now available on personal computers. The object of any wargame (historical or otherwise) is to enable the player to recreate a specific event and, more importantly, to be able to explore what might have been if the player decides to do things differently.
To be a wargame, in our sense of the word, the game must be realistic. And in some cases, they are extremely realistic, realistic to the point where some of the wargames are actually used for professional purposes (primarily the military, but also business and teaching).
Computer wargames have largely (but not entirely) displaced paper (or "manual") wargames. The personal computer brought a lot of new capabilities to wargames and it took about as long as was needed for wargamers to get PCs for the majority of them to shift most of their gaming from paper to keyboard and CRT. PC ownership by wargamers went from less than one in ten in 1980 to over two thirds in the early 1990s. The generally well educated and affluent wargamers joined many other PC users in using computerized wargames. The widespread use of PC based wargames has created a much larger audience for wargamers. A lot of this has to do with the fact that it's much easier to get into a computerized rather than a manual wargame. Moreover, computers made possible some types of wargames, namely simulators, that were simply not practical (or possible) as manual games.
Another development since 1980, one already underway since the late 1970s, was the popularity of fantasy role-playing games (FRPGs or RPGs). Dungeons & Dragons is the most famous of this genre, although it was displaced by card based fantasy games (Magic) in the 1990s. . These games have their origins in wargames: the first ones were simply variations on existing wargames. Many wargamers, particularly the younger ones, dropped the mainline (historical) wargames for FRPGs and then moved on to the computerized versions of FRPGs when PCs became more prevalent. Through the 1980s, however, it became common to see FRPG gamers wander over into wargaming, particularly the computerized type. The common thread here was that there was no immense set of game rules to be committed to memory. While computer wargames are a bit more complex to learn than many other types of computer games, they are much easier to get into than manual wargames.
Computer wargames are more difficult to learn than other computer games because wargames are, at heart, simulations of real life events. A simulation is, by its nature, a potentially very complex device. This is especially true of historical simulations, which must be capable of recreating the historical event they cover. Recreating history imposes a heavy burden on the designer, and the player who must cope with the additional detail incorporated to achieve the needed realism. Most computer wargames are also designed to allow the user to play against the computer. This means that the program must have a pretty good artificial intelligence (AI) system. The more recent computer wargames have AI for both sides, and often have the option of letting the computer play both sides, turning the game into a rather unique form of video entertainment.
In this last respect, computer wargames have merged with many of the recent professional wargames. The US Department of Defense (DoD) has been the primary proponent of computerized wargames since the 1950s. Until the 1980s, DoD wargames paid little heed to the use of history, as most of their gaming was for battles not yet fought. The older DoD gamers were of the "black box" variety. You put a lot of formulas and numbers in the computer and got a lot of numbers back. During the 1980s, the military began to study history once more and now their games often appear very similar (although a lot more expensive) than the ones you can buy in a software store. The military also uses a lot of manual wargames, and these too have been heavily influenced by the commercial wargames that became so common from the 1960s. In fact, one reason why the 1980 edition of this book stayed in print for over ten years was because many military schools were using it as a textbook for courses on wargame design.