A Crisis of Population Density

http://en.wikipedia.org/wiki/Mongol_Empire#Silk_road

"With rare exceptions such as Marco Polo or Christian ambassadors such as William of Rubruck, few Europeans traveled the entire length of the Silk Road. Instead traders moved products much like a bucket brigade, with luxury goods being traded from one middleman to another, from China to the West, and resulting in extravagant prices for the trade goods."

I imagine that this would be the case within Eastrealm, and even moreso between the other Realms of Man (Khemet & Rokugan). It might take less than a fortnight to sail from Helsmuth to Laveril, but overland travel is much slower and more dangerous. Merchant caravans would carry goods that could not be produced locally, and travel back and forth between adjacent cities.