I think because it's an older book, the language is a bit difficult/vague. It's not engaging like a lot of nonfiction authors write these days. I couldn't finish it because it just dragged. I've been "currently reading" this book for over a year and now I'm convinced I won't ever finish. I wanted to read it before Dunkirk the movie came out (yes, that long ago), but even giving myself a month to read it, I couldn't finish. Disappointed that it wasn't as great as I imagined it was going to be.
However, there is a lot of fact-spitting, so if you're interested in that type of reading, then this may be for you.