Her PhD (1975) analysed German right-wing and militaristic nationalism on the basis of the works by Ernst Jünger and his associates.
Hietala's doctoral dissertation paved the way for using content analysis and statistical methods in Finnish historiography.
Hietala's doctoral work brought her into close contact with the school of thought on the history of ideas headed by Professor Aira Kemiläinen at the University of Jyväskylä.
She then moved on to serve as an Assistant in the Department of History at the University of Helsinki and as a Senior Researcher of the Academy of Finland.
Hietala's parents Nikolai and Maire Puusa were evacuees from the part of Finnish Karelia ceded to the Soviet Union in the Second World War.