Professor at Basel (1869–78)

In part because of Ritschl's support, Nietzsche received a remarkable offer to become professor of classical philology at the University of Basel in Switzerland. He was only 24 years old and had neither completed his doctorate nor received a teaching certificate. Despite the fact that the offer came at a time when he was considering giving up philology for science, he accepted. To this day, Nietzsche is still among the youngest of the tenured Classics professors on record. Before moving to Basel, Nietzsche renounced his Prussian citizenship: for the rest of his life he remained officially stateless.
Nevertheless, Nietzsche served in the Prussian forces during the Franco-Prussian War (1870-1871) as a medical orderly. In his short time in the military, he experienced much and witnessed the traumatic effects of battle. He also contracted diphtheria and dysentery. Walter Kaufmann speculates that he might also have contracted syphilis along with his other infections at this time. On returning to Basel in 1870, Nietzsche observed the establishment of the German Empire and Otto von Bismarck's subsequent policies as an outsider and with a degree of skepticism regarding their genuineness. His inaugural lecture at the university was "". Nietzsche also met Franz Overbeck, a professor of theology who remained his friend throughout his life. Afrikan Spir, a little-known Russian philosopher responsible for the 1873 Thought and Reality, and Nietzsche's colleague the famed historian Jacob Burckhardt, whose lectures Nietzsche frequently attended, began to exercise significant influence on him during this time.
Nietzsche had already met Richard Wagner in Leipzig in 1868 and later Wagner's wife, Cosima. Nietzsche admired both greatly and, during his time at Basel, he frequently visited Wagner's house in Tribschen in Lucerne. The Wagners brought Nietzsche into their most intimate circle and enjoyed the attention he gave to the beginning of the Bayreuth Festival. In 1870, he gave Cosima Wagner the manuscript of "The Genesis of the Tragic Idea" as a birthday gift. In 1872, Nietzsche published his first book, The Birth of Tragedy. However, his colleagues within his field, including Ritschl, expressed little enthusiasm for the work, in which Nietzsche eschewed the classical philologic method in favor of a more speculative approach. In his polemic Philology of the Future, Ulrich von Wilamowitz-Moellendorff dampened the book's reception and increased its notoriety. In response, Rohde (then a professor in Kiel) and Wagner came to Nietzsche's defense. Nietzsche remarked freely about the isolation he felt within the philological community and attempted unsuccessfully to transfer to a position in philosophy at Basel instead.
In 1873, Nietzsche began to accumulate notes that would be posthumously published as Philosophy in the Tragic Age of the Greeks. Between 1873 and 1876, he published four separate long essays: "David Strauss: the Confessor and the Writer", "On the Use and Abuse of History for Life", "Schopenhauer as Educator" and "Richard Wagner in Bayreuth". These four later appeared in a collected edition under the title Untimely Meditations. The essays shared the orientation of a cultural critique, challenging the developing German culture along lines suggested by Schopenhauer and Wagner. During this time, in the circle of the Wagners, Nietzsche met Malwida von Meysenbug and Hans von Bülow, and also began a friendship with Paul Rée, who in 1876 influenced him into dismissing the pessimism in his early writings. However, he was deeply disappointed by the Bayreuth Festival of 1876, where the banality of the shows and baseness of the public repelled him. He was also alienated by Wagner's championing of "German culture", which Nietzsche felt a contradiction in terms, as well as by Wagner's celebration of his fame among the German public. All this contributed to Nietzsche's subsequent decision to distance himself from Wagner.
With the publication in 1878 of Human, All Too Human (a book of aphorisms ranging from metaphysics to morality to religion to gender studies), a new style of Nietzsche's work became clear, highly influenced by Afrikan Spir's Thought and RealitySafranski, Rüdiger (trans. Shelley Frisch). Nietzsche: A Philosophical Biography, p. 161. W. W. Norton & Company, 2003.
"This work had long been consigned to oblivion, but it had a lasting impact on Nietzsche. Section 18 of Human, All Too Human cited Spir, not by name, but by presenting a 'proposition by an outstanding logician' (2,38; HH I §18)." and reacting against the pessimistic philosophy of Wagner and Schopenhauer. Nietzsche's friendship with Deussen and Rohde cooled as well. In 1879, after a significant decline in health, Nietzsche had to resign his position at Basel. (Since his childhood, various disruptive illnesses had plagued him, including moments of shortsightedness that left him nearly blind, migraine headaches, and violent indigestion. The 1868 riding accident and diseases in 1870 may have aggravated these persistent conditions, which continued to affect him through his years at Basel, forcing him to take longer and longer holidays until regular work became impractical.)