Complex sentence: Bush's increasing political commitment marked the character of much of the music he produced during the later part of the decade--an exception was the Concert Piece for Cello and Piano, written for the 1937 Paris festival of the International Society for Contemporary Music.
Split into simpler sentences: Bush's increasing political commitment marked the character of much of the music he produced during the later part of the decade. An exception was the Concert Piece for Cello and Piano, written for the 1937 Paris festival of the International Society for Contemporary Music.