Have you played twister ? The games difficulty level increases as the amount of people play it.
The same hold with nations and their National Interests. The more nations you have the more conflicts of national interests will take place. As more nations become progressively developed their aspirations will increase and so will their National Interest conflict.
In the future the concept of nations will be absolete due to this. Instead we should divide the world based on something neutral like climate or race or our favorite football team. So if we have only 6 nations in the world we will be in a better position to help each other as we will have fewer national interest to worry about.
Any takers ?