The stuff of empires. Here are the original 3 books that began the whole thing as well as the first supplement. For those who do not know, players would take the part of a fantasy adventurer and enter dungeons in search of treasure while battling all sorts of foul creatures. One player, the dungeon master, would moderate the game and perhaps even craft his own dungeons and fantasy worlds. At the time I bought this, the game was not too well known but it sure caught on quickly.
Perhaps one of the things that binds the most popular games is introduced here. Players craft their characters, building a little game-playing avatar who goes for a romp in an imaginary world, not unlike the point-based armies created for games like Warhammer and WRG Ancients. By creating these imaginary persons or armies, one invests in it and is anxious to see how it fares.
It is surprising that a game shaped by miniatures rules in this case Chainmail should neglect that side of the hobby. TSR and Gary Gygax did provide Swords and Spells as a kind of Chainmail ver 2.0. But it was not enough to satisfy and the niche left open allowed all sorts of modules for single and massed combat to be concocted by other companies. Eventually, there was an effort to generate a more compelling set of rules but by then most gamers had found other approaches.