[3] Returned to Denmark, he lectured on Native Americans in the United States and their former way of living, and began his studies under Hans Peder Steensby, ethnographer and professor of geography at the University of Copenhagen.
For two years, between 1912 and 1914, Hatt and Demant visited northern Sweden several times, collecting ethnographic materials for the National Museum of Denmark.
[5] In 1919, Hatt was hired to be the inspector at the National Museum of Denmark's Ethnography Department, and he remained at this civil service post for ten years.
Hatt became a public figure in the late 1930s through the early 1940s with his geopolitical analyses that communicated through radio, newspaper, books and journal articles.
During the World War II German occupation of Denmark, Hatt joined the Danish-German reconciliation, possibly because he saw Germany as a natural and inevitable bulwark against Russian communism.
After Denmark's liberation, Hatt was brought before an official court, was found to be engaged in ‘dishonourable national conduct’ during the German occupation, and was dismissed from his university chair, albeit with full pension.