The Spanish Civil War: Historomic
This is one of my favourite historical facts. There’s a lot more where this came from because history is everything that has ever happened. My source material is:
The Battle for Spain: The Spanish Civil War 1936-1939 by Anthony Beevor
Another excellent book that I suggest is Homage to Catalonia by George Orwell. It consists of his personal experiences of fighting for Republican forces in 1936-37.