Avalon Hill meant by that was Japan, for this was one of the then-controversial "RuneQuest Earth" historical sourcepacks of the mid-1980s that did away with the talking ducks and intelligent vegetable elves of Glorantha in an attempt to get gamers to see RQ as a - what could we call it? I know: as a generic universal roleplaying system.
Surprisingly, sourcebooks for 1930s America (Land of the Bowery Boys), 1970s England (Land of Morris Dancers) and the 19th century Raj (Land of the Thuggees) did not follow. But ninja were like hot cakes to the mid-eighties roleplaying market. Ironically, you saw them everywhere.
In the scramble to create the modern mythology of medieval Japan, game publishers weren't too bothered about the details. They just wanted to print the legend. When Jamie and I submitted Tetsubo to a roleplaying company (who shall remain nameless) we were told, "We don't want a simulation of medieval Japan right down to [sic] the level of the Japanese people themselves." In short, can we have Caucasian samurai, midriff-baring geisha, and clans of professional assassins? This thing has to sell to 15-year-old kids in Peoria, you know.
My litmus test was how a game referred to seppuku, a self-sacrificial act carried out to expunge shame or to admonish a lord. As it's not a crime, you do not "commit" seppuku, you "perform" it. A lazy designer, not taking the trouble to think their way inside the culture, invariably used the former. Will the court please refer to Exhibit B, the back cover of the Land of Sushi sourcebook, below? And I rest my case.
Now the confession: this post isn't really because I have any interest in old RQ sourcebooks. I just noticed Land of Ninja in a box in my wife's study last night (she's selling it on eBay) and it reminded me of a big announcement that's coming up on the Fabled Lands blog tomorrow. Nothing to do with Japan, RuneQuest or seppuku, but everything to do with the sneaky fellows in split-toed sandals. Easy, tiger.