Sengoku actually came about completely because of Bushido, and its enjoyment by its fans. Essentially Sengoku "is" Bushido (updated/upgraded a bit). There are a lot of politics and whatnot behind the story that I can't really share here.

One of the contributing factors to the success of Sengoku is that one of the authors is a degreed Japanese historian if memory serves and therefore it allowed the setting to really be ramped up a lot and the depth and feel were dramatically enhanced by his input.

Needless to say I loved Bushido as well, and still hold out hope that one day we'll be able to resurrect Sengoku and bring it back into the lime light.