Oh, yeah there are alot of dangers on the sea now. So, that would be exciting.
Trade routes on land, between citites that are connected by land, will also be fun.
One of the things that would be necessary, would be a way to remove a boat or destroy it completely and having some type of creature that could come up and swallow the boat or even being able to just shoot at it and completely remove it, would be a necessity for trade routes to work.
Or even, possibly finding ways for ships to push other ships out of the way to prevent blocking.
If farming was so deeply connected to cities and war, it also might be essential to feed troops for types of bonuses. An example might be: For a warring city to already have stationary guards, walls, and other defense capabilities.
Strongholds placed within cities or outside of cities might also contain a radius of protection or a type of allowance of protection depending on supplies, so that these forces could also directly affect a faction.
So, the town guards who apply normal Justice would also affect warring guard soldiers because there would be a decrease in the total number of guards. So, if both the city supplies and stronghold supplies were low, a city could be easily captured or over run by enemy forces.
So, caravans and ships and even cities could possibly be pilaged and the enemy could begin transporting goods out of the city.
So, some cities could become key players in rebuilding other cities resources. For example: If every city was depleted to its' minimum resource, it would become necessary to gather resources from all of the cities.
So, if you had an NPC farm in Yew and an NPC winery and produced wine, then to replenish a city without wine, you would need to transport that resource from Yew.
So, that holding or capturing certain cities could deplete resources.
Also, it would be in your interest to possibly destroy farms so that they could no longer produce resources or fail to produce any resources.
And again, there would be a minimal that city could fail, so that there would still be a functional world, such as, a bank, a tailor, a blacksmith but only certain cities would have these resources at their minimum.
Maybe, iron ore could be collected and maintained at a certain level to allow for the smith shop or NPC to be working as leather to the tailor, gold to the banker, and so on.