Why did Friedrich Nietzsche resign from his professorship at the University of Basel?

Friedrich Nietzsche resigned from his professorship at the University of Basel on June 14, 1879, primarily due to his steadily deteriorating health.1

His physical decline began in 1870 after he contracted dysentery and diphtheria while serving as a volunteer medical orderly during the Franco-German War, which permanently damaged his health. By 1871, he had already begun seeking relief from his teaching duties, and he eventually requested and received sick leave in 1877 before his final resignation two years later. Upon his resignation, the university granted him a pension of 3,000 Swiss francs per year for six years.1