A: The West (or America)
C: Western (or American) Buddhism
This diagram is a lie. Or, at least, an untruth, an inaccurate depiction of a cultural-historical phenomena.
A better representation of reality may be something like this, times twenty, a diagram that would take into account the diversity of sub-cultures within the West (or America) and how those sub-cultures interact with and adapt a diversity of Buddhist traditions in dozens of complex ways. An accurate diagram would look more like a fractal, something I can’t draw with a Sharpie, and something that should not be described with a singular noun.