In chapter 15, Robert Wright talks about international organizations gradually growing in power until they turn into something like a world government that can keep the peace globally. He wasn't naive though, especially considering the book was published before 9/11. He mentions that Immanuel Kant was talking about a similar idea right before Napoleon did his thing.
Sooner or later, every successful government comes to consider international chaos a threat. It seems that there are two memes for dealing with it knocking around the global brain. One is the one he discusses in chapter 15. He also mentions the other here and elsewhere - empire.
It seems that governments which give more freedom and more protection to their rights to citizens often become economically much stronger than their neighbors, so much so that they can defeat any likely combination. In the short term at least, while freedom and rights make for a strong nation, they are not the easiest way to deal with threats internationally. If you are militarily able to defeat any threat, why not do so? If you know you can win, but you're not sure what the outcome of multilateral negotiations will be, the choice seems clear. Somehow, when you feel threatened by another entity, negotiation doesn't provide the same lasting and complete sense of security as does a crushing military victory. Certainly, the leader who initiates such a campaign benefits from it, since successful democracies tend to get behind their leaders in wartime.
Rome arguably did very well from this policy. The fall of the Roman empire is worth studying, but Rome was an unchallenged superpower far longer than we have been. It seems that empires since the days of Rome have run into difficulty much faster though, even with similar economic and military preeminence. The British empire was closest to our era technologically, culturally, and morally. Like us and unlike the Romans, they had qualms about genocide for repeated troublemakers. Collective punishment was part of the key to the success of the Delenda est Carthago ethic - rebels might be willing to die, but as Stalin knew, less willing to bring death to their families and neighbors and countrymen.
In Roman times, land was much nearer to being the ultimate definition of wealth than it is today. When the Romans conquered a country, they always have to guard it completely at their own expense. Land could be expropriated, and most people knew something about farming, since most of the population was somehow engaged in it. Even with the risk that the colonists would be slaughtered before Roman troops could arrive to avenge them, many Romans would consider this a good deal. There are several reasons why this would not be practical for the United States today, especially in the countries it is currently concerned about.
The British empire ran into a problem that might not be inevitable, but seems likely to repeat itself if no thought is given to avoiding it. When other nations interfered in the administration of a conquered province, the easiest solution was to conquer these nations too. Of couse this created new borders, and new neighbors who might become troublesome enough to require military action. Each conquest seemed to new proof of power, a new asset and a new buffer. Yet in the long term British power was spread thinned and thinner, and the number of enemies they had to deal with multiplied, while the life blood of their soldiers was leeched away generation after generation.
History need not repeat itself - if we are determined that it not do so. What is most urgently required is to see faraway occupied countries as a military weakness rather than a military strength. If we disdain empire not merely on moral grounds but on practical ones, we are capable of avoiding the fate of the British empire. What is most strongly required is a public perception that a conquest is not a triumph, but the partial amelioration of a failure of a type of which too many can be fatal. If we are not willing to accept that Syria may ignore our demands, we must be careful indeed what demands we make. We must all unite in war time, but once the war is over we should not laud the leader who lead us into a successful war. Although a bloodless victory is better than a bloody one, every occupation must be seen as a burden.
Ultimately, a world government or anything remotely similar must have at least one of these prerequisites. Either no nation must be vastly stronger than all the others, or the strongest nation must see empire as a heavy burden, rather than an accomplishment which is only abstained from due to moral scruples.