[jlg23]

Apparently the answer is in the rule book as well (from the WP article):

"The set had rules for two different games, anti-monopolist and a monopolist. The anti-monopolist rules reward all during wealth creation while the monopolist rules had the goal of forming monopolies and forcing opponents out of the game. A win in the anti-monopolist or Single Tax version (later called "Prosperity"), was when the player having the lowest monetary amount has doubled his original stake."