What we call music today has had a convoluted and arbitrary history. Our ears today are accustomed to certain relationships between frequencies that are not entirely obvious or given. All the music one hears on a commercial radio station be it country, jazz, rock or classical uses the same tuning system known as tempered tuning. Naturally intervals that sound in tune are the fifth (C - G) and the octave (C - C). Using an earlier tuning system called just intonation a fifth relates two frequencies with the ratio 3:2. An octave relates two frequencies with the ratio 2:1. Theoretically going up a fifth 12 times should bring one back to the same note 7 octaves higher. Actually due to the mathematics this is impossible. (3/2)12 = 129.746.... where it 'should' equal 27 = 128
So there is a fundamental flaw in the western tuning system. In earlier times this meant that musicians avoided certain keys because they sounded terrible — out of tune. In the Classical era key changes became a common device. The solution was to divide the fundamental error out over all notes which gives us the modern tempered tuning system. To allow the use of all 12 major and minor keys every note is slightly out of tune.
Other cultures use different tuning systems. In Indian music there is no concept of harmony (chords). This is a western construct. Indian classical music is performed over a drone of root and fifth which are tuned exactly. Indian musicians also use microtonal variations in the notes they play over the drone. What a western musician would call pitch bend.
The history of western music from Palestrina to Schoenberg is one of the rise and destruction of the key system. Byrd advised his pupils only to compose in the keys of C major and A minor — the white notes of a piano. The key system peaks with Mozart. Beethoven starts to use dissonance. Wagner takes this as far as it will go.
The 20th Century sees the abandonment of, even hostility towards the key system, finding its fullest expression in the 2nd Viennese school (Berg, Schoenberg, Webern) who used Serialism to avoid a tonal centre. Serialism uses numerical techniques to ensure that no note is perceived as the tonic or root. Stravinsky moved away from earlier melodic forms and emphasised rhythm, turning the orchestra into a vast percussion instrument.
The 21st Century ? That's up to us.