He is best known for his two-volume work The Decline of the West (Der Untergang des Abendlandes), published in 1918 and 1922, covering human history.

Spengler's model of history postulates that human cultures and civilizations are akin to biological entities, each with a limited, predictable, and deterministic lifespan.

[4]: 3–30, 63 [5][3] While the Nazis had viewed his writings as a means to provide a "respectable pedigree" to their ideology,[12] Spengler later criticized Nazism due to its excessive racialist elements.

[15][16] Oswald's elder brother was born prematurely in 1879, when his mother tried to move a heavy laundry basket, and died at the age of three weeks.

[18] Spengler's maternal great-grandfather, Friedrich Wilhelm Grantzow, a tailor's apprentice in Berlin, had three children out of wedlock with a Jewish woman named Bräunchen Moses (c. 1769–1849) whom he later married, on 26 May 1799.

The couple had another five children,[19] one of whom was Spengler's maternal grandfather, Gustav Adolf Grantzow (1811–1883)—a solo dancer and ballet master in Berlin, who in 1837 married Katharina Kirchner (1813–1873), a solo dancer from a Munich Catholic family;[20] the second of their four daughters was Oswald Spengler's mother Pauline Grantzow.

[21] Like the Grantzows in general, Pauline was of a Bohemian disposition, and, before marrying Bernhard Spengler, accompanied her dancer sisters on tours.

Here he received a classical education at the local Gymnasium (academically oriented secondary school), studying Greek, Latin, mathematics and sciences.

Here, too, he developed his propensity for the arts—especially poetry, drama, and music—and came under the influence of the ideas of Johann Wolfgang von Goethe and Friedrich Nietzsche.

[16] After his father's death in 1901, Spengler attended several universities (Munich, Berlin, and Halle) as a private scholar, taking courses in a wide range of subjects.

It was no longer a momentary constellation of casual facts due to national sentiments, personal influences, or economic tendencies endowed with an appearance of unity and necessity by some historian's scheme of political or social cause-and-effect, but the type of historical change of phase occurring within a great historical organism of definable compass at the point preordained for it hundreds of years ago.

Sociologist Max Weber described Spengler as a "very ingenious and learned dilettante", while philosopher Karl Popper called the thesis "pointless".

[27] In 1924, following the social-economic upheaval and hyperinflation, Spengler entered politics in an effort to bring Reichswehr General Hans von Seeckt to power as the country's leader.

He met Hitler in 1933 and after a lengthy discussion remained unimpressed, saying that Germany did not need a heroic tenor but a real hero ".

[35][36] Spengler spent his final years in Munich, listening to Beethoven, reading Molière and Shakespeare, buying several thousand books, and collecting ancient Turkish, Persian and Indian weapons.

In the introduction to The Decline of the West, Spengler cites Johann W. von Goethe and Friedrich Nietzsche as his major influences.

Goethe gave me method, Nietzsche the questioning faculty…[39] Spengler was also influenced by the universal and cyclical vision of world history proposed by the German historian Eduard Meyer.

[38] The belief in the progression of civilizations through an evolutionary process comparable with living beings can be traced back to classical antiquity, although it is difficult to assess the extent of the influence those thinkers had on Spengler: Cato the Elder, Cicero, Seneca, Florus, Ammianus Marcellinus, and later, Francis Bacon, who compared different empires with each other with the help of biological analogies.

When a Culture enters its late stage, Spengler argues, it becomes a 'Civilization' (Zivilisation), a petrified body characterized in the modern age by technology, imperialism, and mass society, which he expected to fossilize and decline from the 2000s onward.

[43] The first-millennium Near East was, in his view, not a transition between Classical Antiquity, Western Christianity, and Islam, but rather an emerging new Culture he named 'Arabian' or 'Magian', explaining messianic Judaism, early Christianity, Gnosticism, Mandaeism, Zoroastrianism, and Islam as different expressions of a single Culture sharing a unique worldview.

Spengler's obscurity, intuitiveness, and mysticism were easy targets, especially for the positivists and neo-Kantians who rejected the possibility that there was meaning in world history.

[46][47] Spengler responded to the claim that socialism's rise in Germany had not begun with the German revolution of 1918–1919, but rather in 1914 when Germany waged war, uniting the German nation in a national struggle that he claimed was based on socialistic Prussian characteristics, including creativity, discipline, concern for the greater good, productivity, and self-sacrifice.

[49] Spengler claimed that socialistic Prussian characteristics existed across Germany that included creativity, discipline, concern for the greater good, productivity, and self-sacrifice.

[50]Spengler went further to demonstrate the difference between priorities held in England and Prussia: English society is founded on the distinction between rich and poor, Prussian society on the distinction between command and obedience...Democracy in England means the possibility for everyone to become rich, in Prussia the possibility of attaining to every existing rank.

[51] In contrast to Marxism, Spengler claimed that "true socialism" in its German form "does not mean nationalization through expropriation or robbery.

For a slogan’s sake to buy up enterprises immoderately and purposelessly and to turn them over to public administration in the place of the initiative and responsibility of their owners, who must eventually lose all power of supervision—that means the destruction of socialism.

The old Prussian idea was to bring under legislative control the formal structure of the whole national productive force, at the same time carefully preserving the right of property and inheritance, and leaving scope for the kind of personal enterprise, talent, energy, and intellect displayed by an experienced chess player, playing within the rules of the game and enjoying that sort of freedom which the very sway of the rule affords….Socialization means the slow transformation—taking centuries to complete—of the worker into an economic functionary, and the employer into a responsible supervisory official.

[12] In 1934, Spengler pronounced the funeral oration for one of the victims of the Night of the Long Knives and retired in 1935 from the board of the highly influential Nietzsche Archive which was viewed as opposition to the regime.

Alexander Bein argues that with these characterizations Spengler contributed significantly to the enforcement of Jewish stereotypes in pre-WW2 German circles.

"[32] Spengler, however, regarded the transformation of ultra-capitalist mass democracies into dictatorial regimes as inevitable, and he had expressed acknowledgement for Benito Mussolini and the Italian Fascist movement as a first symptom of this development.