As a historian, Kostomarov's writings reflected the romantic trends of his time. He was an advocate of the use of ethnography and folksong by historians, and claimed to be able to discern the "spirit" of the people, including "national spirit", by this method. On the basis of their folksongs and history, he claimed that the peoples of what he called Northern or Great Rus' on one hand and Southern or Little Rus' on the other (Russians and Ukrainians, respectively) differed in character and formed two separate nationalities. In his famous essay "Two Russian Nationalities" ("Две русские народности"), a landmark in the history of Ukrainian national thought, he propagated what some consider to be the stereotypes of Russians inclined towards autocracy, collectivism, and state-building, and Ukrai