Arnold Schoenberg was an early 20th century composer who rejected tonality in favor of atonality. He was influenced by both classical and romantic traditions but felt tonality had broken down due to harmonic and motivic developments. Schoenberg helped pioneer the 12-tone technique of composition, where all 12 notes of the chromatic scale are given equal importance and featured in pre-determined rows, providing a highly structured system without a tonal center. His work progressed through early romantic, free atonal expressionist, and serial periods which demonstrated increasing personal expression and technical control.