Current situation

At the moment there is little need for trade while the community wants and asks for more interaction trade between nations. The reason why nations do not need to trade will be explained by the following example.

The plains biome is able to produce the following. Plants: Wheat, Carrots, Potatos, Melons, Pumpkins, Red - and Brown mushrooms. Trees: Oak Trees, Birch Trees and Acacia Trees. Animals: Sheep, Pigs, Cows and Horses.

The problem

The problem with this is that most nations can make most things themselves. Even though other biomes are better at growing a certain plant or breeding a certain animal as can be seen in the spreadsheet. At Amani Kingdom for instance we just grow our own melons, wheat and carrots. Even though other biomes are waaayyy better at growing those plants there is no real reason for us to import them. Making them ourselves is still easyer and cheaper.

An other example would be horse breeding. Horses just get bred nearly anywhere and every nation pretty much does it themselves.

Because of these reasons there is little reason to trade. The only thing that gets traded a bunch is diamonds. Why? For a big part because they are unique which brings me to the solution.

The solution

The solution in my eyes would be to make sure that every biome has atleast two unique things to offer to 'the world'. Unique in the sense that other biomes just can not breed that animal or grow that tree. That way certain items become rare which will lower the supply and nation can't make 'everything' themselves anymore which will increase the demand. My proposal is these adjustments to Realistic Biomes or atleast something along those lines.

Edit: Don't look at the exact adjustments I made and if they are fair or not. I am more curious whether you agree with my analysis of the problem, the solution I came up with and if you think this is a step in the right direction.