After spending months in a sanatorium during the summer and autumn of 1900, Weber and his wife travelled to Italy at the end of the year and did not return to Heidelberg until April 1902.
He would again withdraw from teaching in 1903 and not return to it till 1919.
Weber is best known for his thesis combining economic sociology and the sociology of religion, elaborated in his book The Protestant Ethic and the Spirit of Capitalism, in which he proposed that ascetic Protestantism was one of the major "elective affinities" associated with the rise in the Western world of market-driven capitalism and the rational-legal nation-state.
He argued that it was in the basic tenets of Protestantism to boost capitalism.
This attempt was unsuccessful, in part because many liberals feared social-democratic revolutionary ideals.
At the outbreak of World War I, Weber, aged 50, volunteered for service and was appointed as a reserve officer and put in charge of organizing the army hospitals in Heidelberg, a role he fulfilled until the end of 1915.
Weber's ordeal with mental illness was carefully described in a personal chronology that was destroyed by his wife.
This chronicle was supposedly destroyed because Marianne Weber feared that Max Weber's work would be discredited by the Nazis if his experience with mental illness were widely known.
a new professional association of German economists affiliated with the historical school, who saw the role of economics primarily as finding solutions to the social problems of the age and who pioneered large scale statistical studies of economic issues.
He also involved himself in politics, joining the left-leaning Evangelical Social Congress.