First, it would be a world where no single power has even the hope to become the ruler of the world. What would be different is that there would be several powers with the ability to retaliate against a nuclear first strike. Today these are the US and Russia, in near future China will reach this ability too. In such a world, fighting for ruling the whole world is no longer a good idea. This situation would differ from the Cold War, where both superpowers fought for ruling the whole world for ideological reasons. But even this fight became more or less meaningless after Soviet Union has reached the ability to retaliate. With world rule impossible, the US hyper-investment in military becomes meaningless. It would no longer allow to gain a lot. Those under attack by one of the poles would ask the others for protection. This was impossible in the Cold War, a capitalist state was unacceptable as an ally for the Soviets, a communist state for the US. Today, we already see around Qatar some sort of alliance of Turkey (Sunni), Iran (Shia) and Russia (orthodox). So, we have an increasing political flexibility for small states too, and pressuring them with military becomes less reasonable too. To reach the point where the US will cut its military to an appropriate size (which is not more than the next 7 powers together) and stops its general aggression against Eurasia (with regime change and terrorism support) needs some time. But with time even the US will learn that regime change no longer works and that terrorism support gives nothing. Once this has been reached, the time of separatism starts. Once big states play no longer a military role, for small and medium states it makes no sense to fight separatism. Only the superpowers may have a problem with this. But even they can solve the problems with separatists by decentralization of almost everything except the military. Formally, the return to classical international law would be the main point of a transition. Actually, we have only weak remains of international law, but de facto the law of the jungle. With Russia and China following their old imperial traditions, which did not include aggression against its neighbors, and the US returning to isolationism, the superpowers would have no objections against a revival of international law, and everybody else would readily submit. The only difference to classical international law would be no right of declaration of war without justification.