Book for my younger brother's birthday?

He's just gotten into reading after being against it since I can remember so I want to get him a book to encourage his new hobby ;) He loves historical nonfiction novels and his interests are in asian history or assassins and stuff. Two books he recently bought are Three Kingdoms: A Historical novel by Guanzhong Luo and The Templars and Assassins: The Militia of Heaven by James Wasserman if that helps you understand his interests at all. He's going to be 18 and I was wondering if anyone had read any good books that follow his interest. I'm pretty ignorant in this area of literature so anything helps, thanks! :)