I'm pretty sure the premise you cite wasn't his view. For Spengler, cultures were attached to a specific location or landscape -- the idea of them spreading doe

I'm pretty sure the premise you cite wasn't his view. For Spengler, cultures were attached to a specific location or landscape -- the idea of them spreading doesn't make sense in that context. I also don't recall any discussion of competition. Here's a direct quote: "A Culture is born in the moment when a great soul awakens out of the proto-spirituality ( dem urseelenhaften Zustande ) of ever childish humanity, and detaches itself, a form from the formless, a bounded and mortal thing from the boundless and enduring. It blooms on the soil of an exactly definable landscape, to which plant-wise it remains bound. It dies when this soul has actualized the full sum of its possibilities in the shape of peoples, languages, dogmas, arts, states, sciences, and reverts into the proto-soul." Spengler, Oswald. Decline of the West: Volumes 1 and 2 (Kindle Locations 2294-2297). Kindle Edition.