Oswald Spengler

German historian and philosopher who wrote The Decline of the West — arguing that civilizations (cultures) pass through organic life cycles (spring, summer, autumn, winter) and that Western civilization had entered its winter phase (Zivilisation), characterized by materialism, cosmopolitanism, and Caesarism.

Created the most influential modern theory of civilizational decline — Spengler's morphological method (each civilization has its own distinctive 'style' running through all its expressions) and his prediction of Western decline through mass democracy, money-power, and Caesarism anticipated the 20th century's political crises.