For 500 years, approximately from the 15th through the 19th centuries, music experienced a progressive exploration of the circle of fifths: the relationships between tonal centers and those tones most closely related to the pedal tones. By the end of that period, formal music had expanded in complexity until the concept of tonal center collapsed and all twelve notes in a scale gained equal value in compositions (Wagner, Mahler). Twentieth century composers who were still attached to the early concept of tonal center composing literally found themselves unable to compose music. New stop-gap and somewhat desperate alternatives were invented, principally among them twelve-tone scale compositions. These were short-lived, highly mechanical explorations of non-tonally centered compositions. Turn of the twentieth century composers like Debussy and Ravel chose to use fully chromatic music (no tonal center, or very minimal) to create "impressionistic" music inspired by the work of painters of their period; composers like Stravinsky and Bartok on the other hand, replayed the old tonal-centered model with a strong emphasis on rhythms and folk melodies. More recently, composers have begun devising retro reinventions of nineteenth century music combined with influences from other cultures; Philip Glass, Steve Reich and John Adams are examples.
Where does music go from here? Techno could be considered the extreme anarchic reaction to all this: music that deliberately and loudly destroys all sentiment for old models and places music firmly in the realm of physicality and sexuality; "IDM", intelligent dance music, then promptly emerged as a necessary antidote, whispering to us with modulated beats and subtle suggestions that validate our intellects as well as our bodies. That's where I believe the heart of music is at the moment. Where will it go next?
All of this is leading me to the conclusion that music, as a human form of expression, is deathless but constantly evolving; that its evolution is shaped by and reflects the evolutionary nature of human consciousness, especially as it's shaped by the encroachment upon our sensibilities by "civilization". I once thought music was doomed; I've never thought humanity is doomed, except that our relentless overpopulation of the planet must lead to vast reductions in our numbers, and that the soul of music is spiritual and celebratory (the chapel and the pub are its father and mother, respectively) and that "folk music" will always rebirth itself in every culture, large or small, springing forth like sudden flames from the earth around us, our own and best spontaneous combustion.