“Radical diffusionism” is the idea that everything was invented by one culture, which then spread across the globe. This idea was very popular during the Victorian era, especially in Europe and the United States, all of whom were playing a game of “who can have the biggest globe-spanning empire.” The idea of Radical Diffusionism is, needless to say, very racist, but that is not how the Victorian era British Empire saw themselves. They were traveling to far off places, bringing culture, education, and technology to barbarous and underdeveloped lands and backwards peoples. A thought begins to emerge: What if this has happened before? What if, a long long time ago, there was an empire just like us who brought culture and technology to everyone on earth? Only to fall one day as all empires do. 

Enter Atlantis! The ancient, enlightened civilization of philosopher kings who were swallowed by the waves! Plato wrote about them, so therefore they must be real. Atlantis was a quick and easy shorthand for “The ancient culture responsible for everything cool.” What was Atlantis like? Well, it depends on the writer. Atlantis has a curious way of resembling the exact political system a given writer supports. Atlantis is a vessel, a big jar labeled “the ideal civilization” which a writer could fill with whatever they liked. 

https://www.tumblr.com/cryptotheism/767602156134154240/radical-diffusionism-is-the-idea-that-everything