The world is already governed by a single force - GREED - without the basic need to have it all there would be a lot more peace.
If I may, I have to disagree just a tiny bit. It's not greed, but rather scarcity of resources. We only have economy because we don't have enough of anything for everyone. There are only two ways to get what we need: 1) by trading in what we have/can produce or 2) by force.
Force is never justified in such cases, yet we routinely see it employed from waging wars to collecting taxes (yes, even taxes voted by majority of people is a use of force against one's private property). And in such cases, shortages are created because it does not change the fact that there isn't enough of resources to be had; it was merely re-distributed from have nots to haves.
If we could have anything we ever wanted, then there'd be no need for economy and consequently no need to exercise force. But such is reality. And IMNSHO, world government just means more exercise of force.