Surrounded by the admiration and esteem of his contemporaries, in 1939 he left Hungary for political reasons and settled in the United States, where he gave lectures and devoted himself to concerts and teaching, without being able to integrate himself entirely in this foreign country. , so much so that a few years later he died in solitude and in the blackest misery.
Influenced at the time of his training above all by the great currents of Central European music, from Brahms to Wagner, to impressionism, Bartok gradually turned to the study of the popular musical heritage of his country, drawing decisive suggestions for his production. In fact, he knew how to blend the advanced techniques of European cultured music, the in-depth and unscrupulous knowledge of the most modern musical trends in Europe of the time, with the awareness that only by drawing deeply on musical folklore would it be possible to create an art free from influence of other civilizations, de-provincialized and at the same time open to the most current problems of language. The Balkan folklore, with its incredible richness of rhythms, melodic movements and modal inflections completely foreign to the tonality, thus provided him with a very solid base on which he could erect a grandiose musical edifice that qualifies him as a composer deeply rooted in the civilization of his country, initiator of a national movement from which very broad developments can be expected.
But Bartòk was too warned a musician not to use this popular "material" in a modernly critical sense.
In his production it is thus possible to recognize the reflection of the great Central European musical culture even after the introduction of the popular element. Suffice it to say that after 1910 he felt strongly the influence of the Viennese brand expressionism, that in some later works the inclination to a neoclassical stylization is evident, which finally, in the last works of his maturity, he seems to aspire to a expansive simplicity of language, in which he definitely appeals to that tone which in some works of the middle period he had almost come to deny or at least to subject to severe criticism.
All this is a testimony of the musician's extremely open mentality, who bends the folkloric material to a type of expression at a high level of art: what in fact constitutes in him the moment of the push forward is precisely this non-superficial relationship with singing and popular dance, this dialectical relationship that allows him to overcome the distress of a material linked to peasant life by transfiguring it into compositions of grandiose developments without betraying its spirit and also profoundly modifying the immediate, in itself almost naturalistic data. Bartòk has indicated which path to follow in the use of popular song in art music: it is a difficult and full of problems path, but it is also the only one that allows to extensively renew the technical means of the modern musician without giving in to a superficial and utilitarian conception of manifestations of popular art.
In addition to orchestral music, Bartòk is also the author of the opera Il Castello di Bluebeard (1918) and of the "scenic actions" Il Principe di legno (1917) and Il Mandarinoarino (wonderful mandarin) (1919); but chamber music also retains a prominent place in his production, in particular the six grandiose quartets (1908-39), the pieces for different instruments and piano and those for solo piano (including the Mikrokosmos, the only method of piano teaching based on criteria of unscrupulous modernity).