The Princes That Were Promised make a pit stop on the Catelyn Stark Memorial Highway- a (fake) highway with tolls every 20 yards, as well as poorly engineered tressels and footbridges that are built so low the tops of SUVs are damaged and 20 car pile-ups occur daily. Before the events of ASoIaF and shortly after a 12-year-old Catelyn Tully was promised to Brandon Stark of Winterfell, Hoster Tully, The Lord of Riverrun and Lord Paramount of the Riverlands, negotiated another marriage pact with Tywin Lannister, The Lord of Casterly Rock and Warden of the West. This marriage would have been more lucrative for Hosterthan the shipment of his eldest daughter to the cold, hard North.
A gigantic step from the Great Houses flirtation with Great-House-intermingling to the Great Houses need for Great-House-intermingling in order to survive.
Idiot's guide to Southron Ambitions- but who is the Idiot? Probably Brandon.