User blog comment:JoshofBlades/Why the Empire Should Prevail Over the Stormcloaks! Part 3 (Economics)/@comment-4583616-20111123201214

Just noticing a little...inconsistency with your lore. Whiterun isn't the city where most trade from the rest of the Empire comes in. Rather, it's central location means that trade passes through Whiterun, only after coming in through the ports of Solitude and Windhelm. The East Empire Trading Company branch in Skyrim is based out of the port of Solitude, so that's where Skyrim sees the largest influx of trade goods. Also, as you mentioned in an earlier blog post, the port of Windhelm is active. So, Ulfric and the Stormcloaks clearly must already be trading with people, before they have even won the war.