In the history of Czechoslovak statehood a constant and fundamental problem has been the definition of the relationship between the two nations, Slovaks and Czechs. It has been common practice for the historiographers of the First Republic (1918–38) and of the present People's Republic, established in 1948, to dwell upon the richness and depth of Czech-Slovak relations prior to 1918. For instance, the Great Moravian Empire was regarded as an early prototype of Czechoslovak unity and statehood. The common aim of the historians was to justify the existence of the Czech-Slovak political union in 1918, to put it on firmer grounds than those of linguistic similarity and geographic proximity. This was considered essential to establish the legitimacy of the bi-national state and to create a strong feeling of Czechoslovak nationalism.