That's the entire point of history classes, and makes a lot more sense than saying "in your first class you will learn every fact between the year 0 and 1000, in your second class between 1001 and 1500, ...". It's much more effective to start off with by providing context, then as minds get more educated to get into details.

The object of high school history wasn't to teach you the names of all the kings of England. It was to give you a context to understand the modern world. [1]

[1] http://www.paulgraham.com/know.html