When God closes the book of human history, anything not done in His name will be forgotten. The centuries and millennia of mankind's collective endeavour to distinguish themselves, to be remembered, to leave an indelible mark or print will slip into infinity where it will burn away in the vacuum of space. God's works, however, will be sung and taught for eternity.
Why, then, do we read about the men and women of the past, especially the ones so consumed with lust for glory that they were driven to acts of supreme evil to secure it for themselves? For the same reason that God has the power and authority to open and shut the book of human history in the first place: history is entirely His.
The Old Testament shows us plainly that God is the main character of everything. Whatever humans do God uses for His purposes. It's not that He steps in when necessary; rather, He is always directly guiding history, making it go the way He intends, bringing it to the completion He's already determined and in which all things will conclude and be brought to consummation.
Studying those whom God has used isn't a useless endeavour. We can spend too much time doing it, and we can study elements of their lives too closely, but in the end reading a biography of a conqueror, politician, statesman, king or queen, or diplomat is simply reading about a particular development in God's plan for humanity. Read about these people—and glorify God and His perfect will.