While best-known for 1984 and Animal Farm, I knew Orwell also had written a few non-fiction books based on his experiences (and thus indirectly how they influenced him). I've just been on holiday, and so bought a couple to read while travelling. Homage to Catalonia is Orwell's story of fighting against Fascism in the Spanish Civil War.
It's almost two books in one. The first part is life on the front, fighting Franco. There are bits in there which somewhat remind me of For Whom the Bell Tolls, although rather more grubby than gritty. Orwell's experiences seem mostly to be of cold, boredom and under-equipment.
The other part, strangely, is the more fascinating. It's about the political in-fighting on the anti-Fascist side, which turned into street-fighting in Barcelona (way to go while trying to fight an external enemy at the same time (!)). Orwell's an ardent Socialist, but a thoughtful and humane one, so he initially tried to ignore the divergence of the Anarchists, Socialists, Communists, etc., and just wanted to fight Frano, but beyond a certain point he couldn't... The organisation he was part of, pretty much by chance, was outlawed retrospectively. People were arrested without charges, prisoners disappeared, and Orwell had to flee the country. The Communists were rewriting history to destroy their enemies (and the international press believed their version!), in the process condemning to death faithful anti-Fascist soldiers. One can start to see where 1984 came from.
While the horrors of totalitarian states are well-known, I still found this an eye-opener in terms of how quickly and unpleasantly things can turn when revolutionary politicians are willing to destroy innocent people in the name of political expediency. The fact that this happened even within the wider context of a civil war, fighting against another brand of totalitarianism, makes it all the more shocking.