His early work in linguistics was on the Mon-Khmer languages of Southeast Asia, which led him to hypothesize the existence of a broader Austric group of languages, connected to the Austronesian language group.
From 1912 on, Schmidt began to publish his 12-volume Der Ursprung der Gottesidee, 'The Origin of the Idea of God', and developed his theory of primitive monotheism, the belief that primitive religion among almost all tribal peoples began with an essentially monotheistic concept of a high god — usually a sky god — who was a benevolent creator. Schmidt theorized that human beings created a God who was the First Cause of all things and Ruler of Heaven and Earth before men and women began to worship a number of gods.[1]
In 1906, Schmidt founded the journal Anthropos, and in 1931, the Anthropos Institute, both of which still exist today. In 1938, Schmidt and the Institute fled from Nazi-occupied Austria to Fribourg, Switzerland.
His works available in English translation are: The Origin and Growth of Religion (1931), High Gods in North America (1933), The Culture Historical Method of Ethnology (1939), and Primitive Revelation (1939).
Schmidt, Wilhelm. 1906. "Die Mon-Khmer-Völker, ein Bindeglied zwischen Völkern Zentralasiens und Austronesiens", 'The Mon-Khmer peoples, a link between the peoples of Central Asia and Austronesia'. Archiv für Anthropologie, Braunschweig, new series, 5:59-109.
Schmidt, Wilhelm. 1930. "Die Beziehungen der austrischen Sprachen zum Japanischen", 'The Connections of the Austric Languages to Japanese'. Wien Beitrag zur Kulturgeschichte und Linguistik 1:239-51.