The term is "postwar" literally but is generally understood to mean post-WWII. I actually considered translating it that way but thought maybe it was still implied (and, technically, WWII was not mentioned by name in the text, as far as I remember). I did some research in translating that part though, and the "postwar economic boom" is a thing that really did happen in Japan after WWII, enough that it had a whole wiki article.

Just to clarify that since it's an issue with my translation more than with the text itself.