Books on Geopolitics, geostrategy, strategy and war.

I've been a military enthusiast since I was a kid. I always loved military stuff. But nowadays I'm looking to expand my horizons and develop a better understanding of geopolitics, geostrategy, strategy and war. I want to have a good understanding of these subjects.

I would love to hear about you guys' favorites and why you like them too!

P.S. To be more specific (it says to do that in the sub rules), I'm a 23 year old guy from Tunisia (North Africa) and I haven't read many books before other than a few military field manuals and some books for school. I'm looking to get into the hobby of reading, and I wanna start with these subjects.