Among the Mighty Five's most notable compositions were the operas The Snow Maiden (Snegurochka), Sadko, Boris Godunov, Prince Igor, Khovanshchina, and symphonic suite Scheherazade. Many of the works by Glinka and the Mighty Five were based on Russian history, folk tales and literature, and are regarded as masterpieces of romantic nationalism in music. This period also saw the foundation of the Russian Musical Society (RMS) in 1859, led by composer-pianists Anton (1829–94) and Nikolay Rubinstein (1835–81). The Mighty Five was often presented as the Russian Music Society's rival, with the Five embracing their Russian national identity and the RMS being musically more conservative. However the RMS founded Russia's first Conservatories in St Petersburg and in Moscow: the former trained the great Russian composer Peter Ilyich Tchaikovsky (1840–93), best known for ballets like Swan Lake, Sleeping Beauty, and The Nutcracker. He remains Russia's best-known composer outside Russia. Easily the most famous successor in his style is Sergei Rachmaninoff (1873–1943), who studied at the Moscow Conservatory (where Tchaikovsky himself taught). The late 19th and early 20th century saw the third wave of Russian classics: Igor Stravinsky (1882–1971), Alexander Scriabin (1872–1915), Sergei Prokofiev (1891–1953) and Dmitri Shostakovich (1906–1975). They were experimental in style and musical language. Stravinsky was particularly influential on his contemporaries and subsequent generations of composers, both in Russia and across Europe and the United States. Stravinsky permanently emigrated after the Russian revolution. Although Prokofiev also left Russia in 1918, he eventually returned and contributed to Soviet music. In the late 19th to early 20th centuries, the so-called "romance songs" became very popular. The greatest and most popular singers of the "romances" usually sang in operas at the same time. The most popular was Fyodor Shalyapin. Singers usually composed music and wrote the lyrics, as did Alexander Vertinsky, Konstantin Sokolsky, and Pyotr Leshchenko. 20th century: Soviet music After the Russian Revolution, Russian music changed dramatically. The early 1920s were the era of avant-garde experiments, inspired by the "revolutionary spirit" of the era. New trends in music (like music based on synthetic chords) were proposed by enthusiastic clubs such as Association for Contemporary Music. Arseny Avraamov pioneered the graphical sound, and Leon Theremin invented thereminvox, one of the early electronic instruments. However, in the 1930s, under the regime of Joseph Stalin, music was forced to be contained within certain boundaries of content and innovation. Classicism was favoured, and experimentation discouraged. (A notable