Nietzsche developed a genealogical method for tracing the historical origins of moral concepts, arguing in "On the Genealogy of Morality" that Judeo-Christian "slave morality," prizing humility and pity, arose from the resentment (ressentiment) of the weak against the "master morality" of the strong. He proclaimed the "death of God" as the collapse of the metaphysical and moral foundations of European culture, and developed the notions of will to power and eternal recurrence as responses to the resulting crisis of values.
Intellectual setting
Nietzsche wrote after the death of God had, in his diagnosis, already occurred culturally in a Europe transformed by science and the decline of Christian metaphysical authority, and his critique of morality developed partly against Schopenhauer's pessimism and partly against the nationalist and antisemitic currents of his own family and era, which he explicitly rejected.
Key ideas
Genealogy of morality and master-slave morality
Nietzsche argued that modern moral concepts of good and evil descend historically from a slave revolt in morality, in which the resentment of the weak against aristocratic "master morality" (which prized strength and nobility) recast humility and self-denial as virtues.
Will to power and eternal recurrence
Nietzsche proposed that a fundamental will to power, not mere survival, drives all life, and posed the thought experiment of eternal recurrence—willing one's life to repeat identically forever— as a test of whether one truly affirms existence.
Legacy
Nietzsche became one of the most influential philosophers of the twentieth century, shaping existentialism, psychoanalysis through Freud, and postmodern thought through Foucault, Derrida, and Deleuze, while his work's posthumous distortion by his sister into Nazi propaganda has made the history of its reception a subject of ongoing scholarly correction.