I went through a
RedBook and decided how interested I was based on the factors that commems mentioned.
If you have one for your hometown or home state, that might be an easy addition.
You may be have more historical interest in the Revolutionary War, Civil War, Westward Expansion series, etc. . .
Also when you read about history you may be drawn to certain people. Who wins: Benjamin Franklin or Abraham Lincoln? Christopher Columbus or James Monroe? and so on. . .