George Orwell's Homage to Catalonia is about his experience in the Spanish Civil War, published in 1938. He was there between '36 and '37 I think. It's pre WWII, and I found it very interesting for the same reason you say here: his account doesn't have the benefit of hindsight. The civil war wasn't even over when the book was published. It's very interesting to see his perspective, what things he saw coming, and what things he didn't.