...certainly since 1800 and perhaps since 1500, what is most extraordinary and salient about our global society is primarily economic and scientific, so you cannot do post-1500 history without knowing economics anymore than you can do early Byzantine history without knowing theology.I'm not certain how much economic history music historians should know, but those two dates -- or a generation earlier for 1800 -- do ring all sorts of music-historical bells. They locate moments in which local European musical traditions innovate in connection with reception by new music-consuming classes and simultaneously begin to have reach beyond local communities, across European borders and, eventually, globally.
I have written before that our continuous music-historical memory extends only into the late 18th century, with musical repertoires predating that era all to be re-discovered, and, in their way, remade as contemporary musics. (The various forms of "nationalist" musics that emerge (and continue to emerge) in the past two centuries are less instances of the faithful transmission of local traditions but of local assertion of participation in the global music culture with local colors, often without much traditional precedent.) A partially economic explanation for pre-classical musical amnesia seems reasonable.
Art and literary history already follow economic history and identify modernity roughly with the turn of the 19th century. I'm now curious as to how music came to unique identify modernity with the 20th century. (No, the invention of sound recording can't be the initial impulse for this.) In fact, it might be more than interesting to rethink classical music history since 1789 or so without 1900 as the major turning point, but rather as just another marker of generational change in a more complex historical texture, with waves to and fro greater or lesser complexity, additions of new resources, ensemble or textural density, etc. while paying closer attention to the patterns of geographical transmission and reception.