Personally, I think you need an even mix regarding national and local history. From working on a national level with my own organization, I can tell you that people tend to feel loyalty to their
chapter first. That is what they know, that's their personal experience with and vision of the fraternity. (When you get your fraternity magazine, what do you turn to first? News of your chapter, and if you're an alumni, news of your old college chapter, right?)
So obviously you need to incorporate your national history into members' education. Try and draw parallels between the 2, show members how the 2 connect.
As Barbara said, having loyalty to the national organization is important. To do that, get them involved. Many of our national committees have (and some require) collegiate members. We send 1 college member / chapter to our national convention (we are still small & can do that

).
The two histories are equally important; you wouldn't have the chapter without the national, but the national wouldn't continue to survive without the active chapters.
You've got to teach them to respect both, that the two aren't entirely separate from one another.