I've never understood the opposition to a global government. It always seems to come from conspiracy theorists that lack critical thinking skills. What are we suppose to do? Never become united? Remain separate entities constantly vying and warring for territory and power? Does that really sound like the intelligent thing to do?
Well the idea is that since it's the 21st century and with improved transportation and communications, we no longer really need nation states that are more or less concepts out of the late middle-ages when people were less intelligent, much more religious, etc. The original American state was intended to be more of a service provider and record-keeper instead of a deity like the British crown and its empire. It gets into the question of what do you really need from a service provider today compared to pre-internet, pre-industrialization, etc.
So part of the problem is that most of the world is not as culturally developed as other parts of the world. It's really difficult for people to think beyond the idea of nation states at this point. Nation states are permitted to collect taxes with the threat of violence, and this is very much an old-world concept, for example. And with that you get greedy people stealing money, squandering funds, and so on. If you can get people to view the state as just a service provider and not a false god to worship then this would be progress.
Radical leftists groups, and other groups like the Club of Rome have tried to discuss efforts to set up global management structures. And some already exist. There's a global currency which exists called SDRs (Special Drawing Rights), but it hasn't yet been implemented. The fact is, like Bill Gates barely being able to keep Windows from being bug-free on release, is that a national or international economy is impossible to manage since it is so complex. The prospect usually attracts some pretty dumb-headed people who can't recognize this fact or think that someone could pull it off. But it can't - every socialist state has failed in the past and all you have today are Cuba and North Korea which speak for themselves. The Bretton Woods system, which was a currency value-pegging scheme set up after WWII to manage European debt with the USD, is also now not really being recognized by Russia, Brazil, and China. So all of these efforts to "share and manage" wealth and debt aren't really working now since the world is getting so damn more complex. But the flipside of it is that nobody really wants to start a war for real anymore now. The US still has the largest military in the world be a huge margin, so you can't deny that. But the EU is BARELY working as we can see with its debt problems. In my opinion even if an Anglo-American alliance, or an American-EU alliance were to be set up it would be a resource draining nightmare and the world is just better off with a coherent and stable payments system that is neutral to any single nation state for those who want to participate in civil society. Cooperation and markets will form at a more micro level and things will still get done - but more slowly. For the rest like ISIS who simply don't want to participate, leave the door open if they ever decide they want to behave again, but otherwise just abandon any efforts to appease them or even interact with them. I see no reason why they still get internet service at this point.
ISIS, North Korea, bits of trouble in Europe, Israel/Palestine, there's not much else to worry over. Africa is developing and so is South America. You can probably have missles pointed at these hotspots should anything flare up, but I think civil society will be able to manage otherwise.