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Due to its position as the primary port city of The Riding and the only city that had significant relations with foreign lands, by the time of the founding of the empire, Greenmouth had become the richest and most cosmopolitan of the cities of along the Green River. Due to its standing, Greenmouth had acquired the power of a suzerain and the Baron of Greenmouth dictated foreign policy for all the cities of The Riding as well as setting self-serving, regional economic policy.
However, by 50 AFE, foreign merchants realized that there was more money to be made if they bypassed Greenmouth and travelled upriver to trade for metal ore and artisan products at Highbridge. These relationships caused tension in the Riding as merchants in Greenmouth hired mercenary companies to harass foreign traders and raid their ships while calling at HIghbridgeHighbridge. The Baron of Highbridge responded by extending the walls of his city to enclose and protect the Docks.
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Even up until the current day, small frictions exist between the denizens of HIghbridge Highbridge and other Riding folk as hurt feeling bruised feelings associated with the Siege of HIghbridge Highbridge and the Barons' War linger.