What phrase is used to describe the first era of american popular music in the 20th century?

The phrase Popular Music called Pop music became so popular during twentieth century in America. Gone were the days when music was confined only to music halls and opera houses. Advancement in music led various music artists to gain influence. The emergence of Jazz and Broadway music was well appreciated and gained a lot of prominence in twentieth century.

Pop music expresses the folk music and the black culture and started to gain significance from the mid nineteenth century. It included Broadway tunes and Ballads.

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explanation:

john maynard keynes developed new economic theories in response to the : b) great depression of the 1930s. his theories are so important that they are known as "keynesianism". in his works he supports the idea of a government with deeper involvement and intervention to end the great depression.