[14] Despite the furor over the Frederick book, and not having written a formal Habilitationsschrift (second thesis to qualify for a professorial appointment), Kantorowicz received an (honorary) professorship at the University of Frankfurt in 1930, though he remained in Berlin until 1931.

[17] He remained in Germany until departing for the United States in 1938, when after the Kristallnacht riots it became clear that the situation for even assimilated Jews such as himself was no longer tenable.

[19] After several years, Kantorowicz was finally able to secure a permanent professorship, but in 1950, he famously resigned in protest when the UC Regents demanded that all continuing faculty sign a loyalty oath disavowing affiliation with any politically subversive movements.

[20] During the controversy in Berkeley, two eminent German émigré medievalists working in Princeton, Theodore Mommsen (grandson of the great classical historian) and the art historian Erwin Panofsky, persuaded J. Robert Oppenheimer, director of the prestigious Institute for Advanced Study, to appoint Kantorowicz to the Institute's faculty of Historical Studies.

His association with the elitist and culturally conservative George-Kreis inspired Kantorowicz to undertake writing a sweeping and highly unorthodox biography of the great Holy Roman emperor Frederick II, published in German in 1927 and English in 1931.

The book traced the ways in which theologians, historians, and canon lawyers in the Middle Ages and early modern period understood "the king" as both a mortal individual and an institution which transcends time.

[28] Drawing on a diverse array of textual and visual sources, including Shakespeare and Dante,[29] The King's Two Bodies made a major contribution to the way historians and political scientists came to understand the evolution of ideas about authority and charisma vested in a single individual versus transpersonal conceptions of the realm or the state in pre-modern Europe.

[33] In Frederick II, the ruler was shown to be the founder of the secular state, at that point a new type of political entity that expressed the wishes of a lay culture that had been spreading for a century in Europe.

[37][38] Conrad Leyser, summarizing the controversy in his 2016 introduction to The King's Two Bodies, describes Cantor's account as a "tissue of falsehoods and half-truths", but also a predictable reaction to Kantorowicz's own suppression of his German past.