yeah . . . Advance Wars series hasn't done particularly well in Japan for whatever reason, they didn't even release DoR there (despite the full Japanese text being in the game's data)
You might actually be able to blame 9/11 for this one, I'm dead serious. The first game's release was delayed in Japan because of the terrorist attacks (it came out one day beforehand in America so we almost didn't get it for a while either) and it didn't come out until a compilation with AW2 years later. Maybe the series would have met with more success had the game come out when it was intended to. I don't know how popular the previous Wars games that had come out in Japan were.
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A hare like me couldn't catch up to Black Turtle.