Answer
1918 marked the publication of the first volume of Oswald Spengler's magnum opus, "The Decline of the West." This influential work presented a cyclical theory of history, proposing that civilizations undergo predictable stages of growth, maturity, and decline. Spengler's analysis, which drew parallels between the Roman Empire and Western civilization, resonated deeply with a Europe grappling with the aftermath of World War I and the uncertainties of the 20th century.