Kelsen's doctoral thesis on Dante's theory of the state in 1905 became his first book on political theory.
 In this book Kelsen made explicit his preference for the reading of Dante Alighieri's Divine Comedy as largely based in political allegory.
The study makes a rigorous examination of the "two swords doctrine" of Pope Gelasius I, along with Dante's distinct sentiments in the Roman Catholic debates between the Guelphs and Ghibellines.
 Kelsen's conversion to Catholicism was contemporaneous to the book's completion in 1905.
 In 1908 Kelsen won a research scholarship which allowed him to attend the University of Heidelberg for three consecutive semesters, where he studied with the distinguished jurist Georg Jellinek before returning to Vienna.

The closing chapter of Kelsen's study of political allegory in Dante also was important for emphasizing the particular historical path which led directly to the development of modern law in the twentieth century.
After emphasizing Dante's importance to this development of legal theory, Kelsen then indicated the historical importance of Niccolò Machiavelli and Jean Bodin to these historical transitions in legal theory leading to modern twentieth century law.
In the case of Machiavelli, Kelsen saw an important counter-example of an exaggerated executive part of government operating without effective legal restraints on responsible conduct.
For Kelsen, this would be instrumental in the orientation of his own legal thinking in the direction of strong rule of law government, with a heightened emphasis on the central importance of a fully elaborated power of judicial review.

Kelsen's time at Heidelberg was of lasting importance to him in that he began to solidify his position of the identity of law and state from the initial steps he observed as being taken by Jellinek.
Kelsen's historical reality was to be surrounded by the dualistic theories of law and state prevailing in his time.
The major question for Jellinek and Kelsen, as stated by Baume is, "How can the independence of the state in a dualist perspective be reconciled with its status (as) representative of the legal order?
For dualistic theorists there remains an alternative to monistic doctrines: the theory of the self-limitation of the state.
Georg Jellinek is an eminent representative of this theory, which allows one to avoid reducing the state to a legal entity, and also to explain the positive relationship between law and state.
The self-limitation of the sphere of the state presupposes that the state, as a sovereign power, by the limits that it imposes on itself, becomes a rule-of-law state."
For Kelsen, this was appropriate for as far as it went yet it still remained a dualistic doctrine and therefore Kelsen rejected it stating: "The problem of the so-called auto-obligation of the State is one of those pseudo-problems that result from the erroneous dualism of State and law.
This dualism is, in turn, due to a fallacy of which we meet numerous examples in the history of all fields of human thought.
Our desire for the intuitive representation of abstractions leads us to personify the unity of a system, and then to hypostasize the personification.
What originally was only a way of representing the unity of a system of objects becomes a new object, existing in its own right."
Kelsen was joined in this critique by the distinguished French jurist Léon Duguit, who wrote in 1911: "Self-limitation theory (vis Jellinek) contains some real sleight of hand.
Voluntary subordination is not subordination.
The state is not really limited by the law if the state alone can introduce and write this law, and if it can at any time make any changes that it wants to make in it.
This kind of foundation of public law is clearly extremely fragile."
As a result, Kelsen solidified his position endorsing the doctrine of the identity of law and state.

In 1911, he achieved his habilitation (license to give university lectures) in public law and legal philosophy, with a thesis that became his first major work on legal theory, Hauptprobleme der Staatsrech
Kelsen's doctoral thesis on Dante's theory of the state in 1905 became his first book on political theory.  In this book Kelsen made explicit his preference for the reading of Dante Alighieri's Divine Comedy as largely based in political allegory. The study makes a rigorous examination of the "two swords doctrine" of Pope Gelasius I, along with Dante's distinct sentiments in the Roman Catholic debates between the Guelphs and Ghibellines.  Kelsen's conversion to Catholicism was contemporaneous to the book's completion in 1905.  In 1908 Kelsen won a research scholarship which allowed him to attend the University of Heidelberg for three consecutive semesters, where he studied with the distinguished jurist Georg Jellinek before returning to Vienna.
The closing chapter of Kelsen's study of political allegory in Dante also was important for emphasizing the particular historical path which led directly to the development of modern law in the twentieth century. After emphasizing Dante's importance to this development of legal theory, Kelsen then indicated the historical importance of Niccolò Machiavelli and Jean Bodin to these historical transitions in legal theory leading to modern twentieth century law. In the case of Machiavelli, Kelsen saw an important counter-example of an exaggerated executive part of government operating without effective legal restraints on responsible conduct. For Kelsen, this would be instrumental in the orientation of his own legal thinking in the direction of strong rule of law government, with a heightened emphasis on the central importance of a fully elaborated power of judicial review.
Kelsen's time at Heidelberg was of lasting importance to him in that he began to solidify his position of the identity of law and state from the initial steps he observed as being taken by Jellinek. Kelsen's historical reality was to be surrounded by the dualistic theories of law and state prevailing in his time. The major question for Jellinek and Kelsen, as stated by Baume is, "How can the independence of the state in a dualist perspective be reconciled with its status (as) representative of the legal order? For dualistic theorists there remains an alternative to monistic doctrines: the theory of the self-limitation of the state. Georg Jellinek is an eminent representative of this theory, which allows one to avoid reducing the state to a legal entity, and also to explain the positive relationship between law and state. The self-limitation of the sphere of the state presupposes that the state, as a sovereign power, by the limits that it imposes on itself, becomes a rule-of-law state." For Kelsen, this was appropriate for as far as it went yet it still remained a dualistic doctrine and therefore Kelsen rejected it stating: "The problem of the so-called auto-obligation of the State is one of those pseudo-problems that result from the erroneous dualism of State and law. This dualism is, in turn, due to a fallacy of which we meet numerous examples in the history of all fields of human thought. Our desire for the intuitive representation of abstractions leads us to personify the unity of a system, and then to hypostasize the personification. What originally was only a way of representing the unity of a system of objects becomes a new object, existing in its own right." Kelsen was joined in this critique by the distinguished French jurist Léon Duguit, who wrote in 1911: "Self-limitation theory (vis Jellinek) contains some real sleight of hand. Voluntary subordination is not subordination. The state is not really limited by the law if the state alone can introduce and write this law, and if it can at any time make any changes that it wants to make in it. This kind of foundation of public law is clearly extremely fragile." As a result, Kelsen solidified his position endorsing the doctrine of the identity of law and state.
In 1911, he achieved his habilitation (license to give university lectures) in public law and legal philosophy, with a thesis that became his first major work on legal theory, Hauptprobleme der Staatsrech
Hans Kelsen