Spenglerian

Spenglerian: Spen·​gle·​ri·​an | \ ˌshpeŋ-ˈglir-ē-ən  , ˌspeŋ-, -ˈlir- \ adjective: of or relating to the theory of world history developed by Oswald Spengler which holds that all major cultures undergo similar cyclical developments from birth to maturity to decay

Context: Murray is not putting forward a Spengleria thesis that the collapse of the West is inevitable or that..... Reviling the West by Peter W. Wood, National Review, May 30, 2022, p34.