One of the asymmetries of the current land situation is that nations enjoy only the benefits of land ownership without suffering any of the consequences.
In reality, a large land area implies a large border, which makes a nation militarily vulnerable due to the difficulties in watching over such a large perimeter.
This could be represented in the game by making the number of defensive war slots proportional to a nation's land area.
This neatly represents the idea that a nation with a large area is 'adjacent' to more other nations than a smaller nation would be. The 'cost' of this is having to defend itself from an increased number of potential sources of attack.