Has it ever really existed? The most famously cited exponents, the Nazis, were not really. They believed a sub-group they called Aryans were ordained by nature to rule the world. Sure the Aryans were supposed to be white, but so to were a lot of the subject races. Slavs and Jews, for starters. They hated Black people as well, but did not devote much attention to them because there were so few in Europe. The Nazis were actually obsessing about the hierarchy within white races, not the status of white people over non-whites.
Who else? The Klan? Well once again they seemed to hate White people too. They loathed uppity Blacks. But they could tolerate deferential Blacks, but Jews and Catholics could never be tolerated. So they saw blacks as inferior, but other whites as malicious. In any event they will have seen white people as above black people, but not all White people were among the elect. Besides, let’s face it. The KKK was a scarcely articulated outburst in response to the Civil War, not a thread of history. It did not arise from a pedigree of white supremacy. Just discontented moronic peasantry who were convinced they should be lords, or fallen antebellum aristocracy who thought they should be kings.
An orgy of ego-wound licking.
Most of European history shows White people fighting, conquering, and subjecting other white people. And within nations they were more interested in the hierarchy of White people over other White people. The possibility of White Supremacy is only late. When some lowly tenant had been humiliated by his Lord of the Manor he did not tell himself, “At least I am better than a Black guy!” or look for some Asian to deflect blame to. Hell, ‘race’ was probably unknown to him. But he was sure the people a couple of villages over were lazy, dishonest skinflints who would borrow an ox and work it near to death.
It has only been in the last few hundred years when Black people were a race rather than a novelty. The great sin of slavery (where Europeans cashed in on the slave trade already in Africa but on a grander scale) was driven by economics. Not because black people were inferior, but because they were cheaper than white people. Without slaves they would move straight back to white people (and black – whoever was cheaper) just as they had profited from white people for centuries. And the contempt of the ruling elite was for anyone below them, regardless of colour. Economic supremacy.
But even if there were people motivated by a belief that all black people were inferior to all white people by default (not simply sharing lower rungs with them) then were they a movement? Were they the spirit of an age? I doubt it. From the get go White people were trying to convert Black people to their own faith and their own God. They believed that God wanted them to do that, that God saw them as his Children too. And from the beginning the main current of Europeans was to elevate black people toward equality, and save them from less scrupulous White people. Does that sound like White Supremacy?
It is all just so much bollocks.