Make war, not love is your answer.
You might find too much food in times of peace, reason enough to go to war.
If your realm has a massive surplus, all you need to do is deny other realms their surplus in order to force them to buy it from you.
Obviously it isnt easy to scheme out a massive war leading to food shortages and starvation, you'd need to work together with your fellow players, which is a core design of this game, just as warfare is.
Does that help?
