I think - and people might find this offensive, in which case I apologise - that JKR deliberately allows us to infer that the great fight between Grindelwald's racial purity movement and Dumbledore's liberal humanism (and the Russian Wizards' powerful wand technology?) took many years, caused destruction across the whole world, and that muggle perceptions and memories have been altered by the wizards so that all we remember is that there was a great war 1939-45 in which many millions died.
My son, when I said this to him, said I was accusing JKR of being a holocaust denier. No, I am not. For one thing of course she isn't arguing that any of this really happened, nor is she minimising the suffering and death of real people. Nor is she crudely using the suffering of the war and the other events to gain emotional punch - she handles it delicately at arm's length.
Did anyone find themselves speculating in this way? Or the contrary?