Also, the school subject is kinda supposed to give you general knowledge of most of the general history, and they have X years to do it. Back in school we even had 2 different history subjects in our schedules, where one focused on the history of the world and one was for national history of the country.

While researching history on your own, you are the one who decides how shallow or deep you want to look into something, so it naturally just aligns with stuff that you find interesting.