Bebop and subsequent post-war jazz developments featured a wider set of notes, played in more complex patterns and at faster tempos than previous jazz. According to Clive James, bebop was "the post-war musical development which tried to ensure that jazz would no longer be the spontaneous sound of joy ... Students of race relations in America are generally agreed that the exponents of post-war jazz were determined, with good reason, to present themselves as challenging artists rather than tame entertainers." The end of the war marked "a revival of the spirit of experimentation and musical pluralism under which it had been conceived", along with "the beginning of a decline in the popularity of jazz music in America", according to American academic Michael H. Burchett.