Dutch Uncle
* Tertia Optio * Defend the Constitution
That's part of it, no doubt, but how much history can schools cram into HS students? IIRC, most HS history is American history which includes some global history due to both our heritage and global conflicts.I don't think it's the length of the year.
I think there has always been a systematic bias to focus on the history of northwestern Europe because of our Anglo-British heritage. Teachers really get almost no exposure to the Byzantine Empire, the Polish-Lithuanian Commwealth, or Imperial Russia even in their college education.
World history is more of a college subject...and not much there either for all the arts and music majors.