What harmonic, melodic and rhythmic elements are common in 20th Century Music?

The harmonic elements that are common in 20th century music are the regular use of dissonance, and a lack of classical chord progressions. This dissonance is also unlikely to be prepared as seen with music of earlier eras. There is also likely to be melodic angularity, as well as use of chromaticism in the melodic lines. Many rhythmic techniques are also characteristic of 20th Century music, such as syncopation, and lack of regularity and repetition of rhythm.