I paged through the threads about books on here, but I didn't exactly find what I was looking for. Specifically, I'd like recommendations on good introductory books for COIN. Note two things, please:

1. I already own FM 3-24. I bought it two years ago, and it came along with me to college.

2. I'm in college. So I prefer free things. Free things are nice.

Any other recommendations on books that relate to this sort of thing are welcome (history of radical Islam, history of Afghanistan, etc.).

Thanking you in advance.