20th-century classical music describes art music that was written nominally from 1901 to 2000, inclusive. Musical style diverged during the 20th century as it never had previously. So this century was without a dominant style. Modernism, impressionism, and post-romanticism can all be traced to the decades before the turn of the 20th century, but can be included because they evolved beyond the musical boundaries of the 19th-century styles that were part of the earlier common practice period. Neoclassicism and expressionism came mostly after 1900. Minimalism started much later in the century and can be seen as a change from the modern to post-modern era, although some date post-modernism from as early as about 1930. Aleatory, atonality, serialism, musique concrète, electronic music, and concept music were all developed during the century. Jazz and ethnic folk music became important influences on many composers during this century.
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