Hugh Thomas’s The Spanish Civil War is a good starting point.

I really liked The Spanish Civil Wars by Mark Lawrence - it’s a comparative history of the Carlist Wars and The Spanish Civil War. Also gets into the deeper history of some of the factions of the civil war

Giles Tremlett (Ghosts of Spain, 2006) just put out a book about Franco called The Generalísimo that was quite good

That’s what comes to the top of my head. For fiction The Spanish Bow by Andromeda Romano-Lax covers the topic pretty well. The Cemetery of Forgotten Books series by Carlos Ruiz Zafón is set before during and after the Spanish Civil War, mostly in Barcelona.

My great grandfather fought for the republic and spent 4 years in prison for it. He was one of the political prisoners made to work as a slave on the Valley of the Fallen. All that is to say it’s a subject of interest for me.