Crusade is a supplement for the Starfire 3rd Edition game system. The Starfire series always contained a 'Future History' of 'historical' information and 'historical battles' in the future. This supplement for Starfire 3rd Edition included the scenarios and 'history' covering the Theban War (The designer, David M. Weber, also published a book of the same name, and this scenario book covers the events of the book). - BoardGameGeek