Final Three Eras in Music History

The other three eras in the history of music are labeled as Classical, Romantic and 20th Century.
"Although the Classical Era lasted for only 70 years, there was a substantial change in the music that was being produced. Classical music placed a greater stress on clarity with regard to melodic expression and instrumental color. Although opera and vocal music (both sacred and secular) were still being written, orchestral literature was performed on a much broader basis. The orchestra gained more color and flexibility as clarinets, flutes, oboes, and bassoons became permanent members of the orchestra."
"The Romantic era was a period of great change and emancipation. While the Classical era had strict laws of balance and restraint, the Romantic era moved away from that by allowing artistic freedom, experimentation, and creativity. The music of this time period was very expressive, and melody became the dominant feature. While new instruments were constantly being added to the orchestra, composers also tried to get new or different sounds out of the instruments already in use."
" With the coming of the 20th century another evolution in the musical world emerged. While some of the early 20th century music can be seen as extensions of the late Romantic style, much of 20th century music can be seen as a rebellion. Composers did not look to build on what was standard but again created music freely and used sounds that went against the current grain. Twentieth century music can be described as being more refined, vague in form, delicate, and having a mysterious atmosphere."