Get your facts from nonfiction. That's the right way to do it. One thing I've always believed is that Stalin was a mass murderer, but I've never read any book that dissected his viciousness. I do want to read Timothy Snyder's Bloodlands: Europe between Hilter and Stalin.
But I recently reviewed a book for Kirkus, a novel, which covered another ugly part of mid-20th century history about which I'd been ignorant. The novel is Thomas Cook's The Quest for Anna Klein.
Mentioned as part of the plot was the mistreatment of Spanish Republicans who had fled to France following their defeat in the Spanish Civil War. "Interned" is the most benign way of describing it, although the comparison of that state may be most similar to the manner and condition in which the Imperial Japanese Army "interned" non-combatants.
I knew France, especially Vichy France, did not have a good record when it came to its treatment of Jews during World War II, but I didn't know about the fate of these Spanish Loyalists.