Professor Aram Sinnreich, in his book The Piracy Crusade, states that the connection between declining music sails and the creation of peer to peer file sharing sites such as Napster is tenuous, based on correlation rather than causation. He argues that the industry at the time was undergoing artificial expansion, what he describes as a "'perfect bubble'—a confluence of economic, political, and technological forces that drove the aggregate value of music sales to unprecedented heights at the end of the twentieth century".