Aegyptos,

You have hit the proverbial nail on the head. Barring a dramatic and sudden change in human nature (unlikely anytime soon given the rate of evolutionary change, even when considering the role of mutations in speeding such change) and the way in which human societies organize themselves, the nation-state will remain the basis on which human societies define themselves and on which international relations are based. National interests will continue to play the leading role in defining the world's foreign policies. Safeguarding and promoting, to the maximum extent possible, international peace and security will continue to depend far more on a nation's (and its allies) strength, the balance of power, trade and cooperation between sovereign states, etc., than international or supranational organizations such as the United Nations.

A post nation-state order is highly unlikely anytime soon. Therefore, a world in which global interests transcend national ones is also highly unlikely anytime soon. Instead, truly global interests are quite limited in number i.e., addressing risks presented by nuclear weapons proliferation, pandemics, etc.