I've been looking at TSR's old Birthright setting lately, searching for an easy way to quantify trade between political entities. I'm thinking about ways for a city or region or planet to develop resources, create industries, and trade with other regions. Birthright's guild system is a little clunky so I'm looking for other systems or techniques, especially ones that can work universally since I'd like to use a similar system for Traveller's deep space setting as well.
Here's a fantasy example: a dwarven clanhold decides to develop its iron mining industry. It starts generating surplus iron which can be traded for more food to grow the community. When the community grows, it attracts more smiths to generate surplus armor and weapons to sell at a higher profit for more food and luxury goods. Right now I have no system to quantify any part of this situation, and I fear the day my players focus on unraveling my handwaved economic system.
What game systems, settings, supplements, or online resources contain rules for regional resource management and trading between regions? How do you track and manage your game world's regional economies?