Your question certainly deserves an in-depth look; let's say that within the period known as "the young national schools," in the Scandinavian area—Denmark, Norway, Sweden, and Finland—a musical current linked to national folklore developed during the second half of the nineteenth century.
In Denmark, the musician Niels Wilhelm Gade (1817-1890) stands out, author of the cantata "The Elf King's Daughter" (1854), which is rich in folk themes.
Carl August Nielsen (1865-1931), on the other hand, is a composer of piano, chamber, concerto, and symphonic music that presents a new language close to the new musical trends of twentieth-century Europe.
In Sweden, Franz Berwald (1796-1868) asserts himself as the author of four symphonies written between 1842 and 1845, which demonstrate a sensitivity to certain orchestral effects.
In Norway, the most significant personality is Edvard Grieg (1843-1907); with a German musical education from studies at the Leipzig Conservatory, he shows a keen interest in the musical folklore of his own country and, following his encounter with the great Norwegian playwright Henrik Ibsen (1828-1906), writes the incidental music for Peer Gynt (pronounced Gunt).
His production ranges from Lieder (150) for piano and voice to numerous short pieces for piano included in ten collections of lyric pieces (1867-1901).
Characteristics: a language rich in melodic spontaneity, refined harmonies with the evident influence of folk melodies and Norwegian dance rhythms (see Norwegian Dances op. 72), the piano concerto in A minor (1868), and sonatas for violin and piano.
In Finland, the greatest musical exponent of that period is Jean Sibelius (1865-1957). His compositions feature Nordic folk themes and melodic ideas of folk derivation. The most significant compositions are symphonic poems such as "A Saga" (1892), Karelia (1895), "Finlandia" (1899), and seven symphonies written between 1899 and 1924.
But what are the national schools?
With the revaluation of folk song and national identities, musicians operating during the nineteenth century increasingly turned their attention to the heritage of folk traditions and utilized the expressive resources typical of this repertoire, assimilating them with "art" music. Romantic nationalism, therefore, while preserving the substantial musical structure of the Western tradition, carries out a profound renewal whose effects, at the turn of the century, would produce radical changes. In the Romantic era, the search for and expression of national identity played a determining role in artistic development, especially in those European countries that had established links with the Italian-French-German musical culture.
This occurred in a particular way in Russia where, following the victory over the Napoleonic armies, patriotism and the valorization of the cultural traditions of Slavic peoples were consolidated.
The awakening of national consciousness consequently favored the emancipation of music from Western imported forms through the revaluation of folk heritage and the enhancement of diverse historical/musical traditions. In opera theater, all national characters manifest themselves through the choice of historical/folk, epic/legendary, or fantastic subjects. In instrumental, symphonic, and chamber music, exotic and folkloric elements, folk motifs, and folk dance rhythms are inserted. Even harmonic/modal archaisms and refined, exuberant orchestral effects confer a particular "local color" to the music. Thus, a style is created that is capable of elevating the nation's music and folk song to an art musical language by infusing them with new elements and an authentic "national character." All this happens, however, in respect for and following the formal and stylistic models established by Western musical culture, while grafting onto them all those elements typical of individual realities and folk traditions.
Therefore, there was a great folklore first before that.