As a follow-on to General Mattis' email about reading history, CNAS has a good discussion about what should be read in-between the lines.
http://www.cnas.org/blogs/abumuqawama/2013/05/mattis-book-club.html
As an officer, you have a tool bag that you fit a variety of tools into, and use these tools to fix problems you encounter throughout your day. These tools can be built by training, experience, or reading. If you don't read history, you simply deprive yourself of tools that you could use in your career. However, just like not every problem can be fixed with a hammer, not every problem you'll encounter will get fixed by reading history.
A good example is the Falklands Conflict. I encourage all of my officers to read about the Falklands Conflict (specifically to read One Hundred Days) as a great example of what a modern maritime war might look like in the future. It's not to say modern war WILL look like this...we have so many new technological advances that it will be very different. But the Falklands Conflict shows us how things like initiative and leadership will be demonstrated with technology. Plus, it's a good contrast to the WW2 thinking that seems to prevail everywhere else.
Keep reading, and giving yourself more tools in your tool bag.
