Difference between HL and SL history is a few more subjects, as well as an extra test at the end. As per subjects, IB asks teachers to teach certain categories, and your teacher chooses which specific example he / she wants to teach to satisfy that category. This as consequence makes that in the final IB test, the questions are often vague, such as: “explain the consequences of two conflicts / wars in the 20th century”.
If you like history / learning about the past, I recommend HL. With a good teacher, it can be lots of fun.
Hope this helped, if anyone else sees something I missed feel free to pitch in