Opera is an art form that combines music and text in a theatrical setting. It is one of the main pillars of the Western musical tradition, arising in Italy at the end of the 16th century and soon spreading to the rest of Europe. Being one of the most important musical expressions of the time, it was soon adapted by composers from all regions, which resulted in the development of several styles. Though opera arguably started out as a court practice, it quickly spread to other spheres of popular domain, blending elements of tragedy and comedy. The latter were purged out with the establishment of the so called Opera Seria as the dominant form of opera. However, the excessive musical embellishment and virtuosity that eventually came to characterize Opera Seria led to a subsequent reform by Christoph Willibald Gluck, who advocated that all elements (music, ballet, staging) should be subservient to the overriding drama, and argued for a more austere form of music. One of the defining figures in classical Opera is Wolfgang Amadeus Mozart, who composed both serious and comic operas, and elevated the art to limits with no precedents.
The 19th century saw the rise of several trends (bel canto, verisimo, and several nationalistic styles). Possible the most important contributions to opera were done by Giuseppe Verdi in Italy, and Richard Wagner in Germany, with the latter developing the concept of Gesamtkunstwerk ("complete work of art") which combined music, poetry, theater, and painting, resulting in colossal, philosophically deep works. Wagner redifined the opera as a way of approaching music (and art), and his influence was inescapable.
The 20th century was characterized by several forms of experimentation, including but not limited to serialism, minimalism, and experimentation with electronic music.