Weber's work in the field of sociology of religion began with the essay The Protestant Ethic and the Spirit of Capitalism and continued with his analyses in The Religion of China, The Religion of India, and Ancient Judaism. His work on other religions, however, would be interrupted by his sudden death in 1920, which prevented him from following Ancient Judaism with studies of early Christianity and Islam.[20] The three main themes within the essays were: the effect of religious ideas on economic activities; the relation between social stratification and religious ideas; and the distinguishable characteristics of Western civilisation.[21]