20th Century, 1959-Today: The music of the early 20th century was marked by increasing complexity and abstraction. Serialism and the chance practices of John Cage and his followers created an aesthetic that stood opposed to the Romanticism of the century before. In the '60s and '70s a counter-reaction began to emerge as a new group of young composers sought to free themselves from the strict rules of atonalism and serialism and embrace the simplicity of minimalism.