Do you have any interest in the philosophies of introflection pioneered by Buddhism?

[emjay]

Not knowing much about zen is a good setup for a zen joke.

The book you have is very explicitly about modern revisionist buddhism.  Zen is mahayana.  Or, at least, it started out that way - but it got alot of purchase in the west due to our interactions with japan.  Other (historical) forms lean into tradition and scripture and ritual and dogma, zen leans out.  Zen is the "just sitting" kind (that's where it gets it's name), that regards the pursuit of enlightenment as futile.  Insomuch as there's a cycle of suffering you will be locked into it, no matter how much study or meditation you do.

You can probably see how this appealed to feudal warlords.  

Right, well there's definitely no mention of that in this book; that's the first time I've heard of a Buddhism that considers the pursuit of enlightenment futile. But interesting nonetheless.