This is an amazing book. I've never really read much about the First World War. Anyone who's so much as glanced at my non-fiction shelves or GoodReads stats will note a decided preponderance of works relating to the Second World War, but nothing on the First. Everything I know about the First World War is due to Sue Harsant, who taught me history in high school (and I shall never forget her complaining after an exam/test/assignment that we should not simply say Ferdinand, because she might think we were referring to Ferdinand the Bull who went traipsing through the daisies. Her very dry sense of humour delighted myself and Tiina Napoleon at the time).
Anyway, the point of that long aside was that this is the first work I've ever read about the First World War and so was my first glimpse into the horrors of trench warfare. I had an intellectual understanding that it was a horrific thing, but I didn't understand. I still don't, thankfully, but now I have a greater idea of what about it was so horrific. Of what it was like to be there, what happened to people on the ground. On the one hand it makes me glad for the 'advances' of mechanised warfare. At the same time, those same supposed advances terrify me. No longer does individual kill individual, now machine destroys machine and life from afar. I know they had machine guns and bombs and so on, but on the whole they could at least see who they were killing. The horror of war, and the facts of war - the facts being that you are killing individuals that are really no different from yourself - were up close and personal. They no longer are.
At the same time as this works as a general introduction (for me) to the First World War (because you can be sure I'm going to be looking for more on the subject now), it also works really well as a biographical work on Tolkien. Specifically with regard to the effect that his experiences in the war and in the Battle of the Somme particularly must have had on his writing. You cannot go through an experience of that sort without undergoing profound changes. There's a fair amount of speculation on the author's part because Tolkien was extremely reticent regarding those experiences. That speculation is backed up by fairly solid reasoning (in my completely uncritical opinion) and while I'm of the opinion that you can never know exactly how things influenced the creative process, you can work out a fair amount, especially when it's something as significant as this.
If you're interested in either the First World War or Tolkien, I'd recommend this.