World government is concept about possibility to handle, to rule the development of the human civilization on the Earth from the single office, single council or even by a single dictator.
The Soviet ideas about the "world revolution" assumed that the Soviet Union and the government of the Soviet union play the dominant role in the formation of a world government.
The same idea seem to exist and, perhaps, to dominate in the Nazi Germany and the communistic China, at least in century 20.
Similar ideas are expressed with respect to the USA dominance in 21st century .
Usually, each of defenders of the idea of the 'world government assumes that namely he/she is supposed to play dominant (or at least important) role in that government. The concept of the world government looks similar to those of fascism and usually is considered as something bad. Those who assume the voluntary cooperation of countries at some equal (or compatibel) rights and contribution use the term "international cooperation"  and apply it to the join work in some specific area, for example the scientific research, rather than to a ruling of countries.
- http://www.dailysquib.co.uk/index.php?news=3089 Alfred Heinz. Henry Kissinger: "If You Can't Hear the Drums of War You Must Be Deaf". 27/11/2011 09:40. "We told the military that we would have to take over seven Middle Eastern countries for their resources and they have nearly completed their job. We all know what I think of the military, but I have to say they have obeyed orders superfluously this time. It is just that last stepping stone, i.e. Iran which will really tip the balance. How long can China and Russia stand by and watch America clean up? The great Russian bear and Chinese sickle will be roused from their slumber and this is when Israel will have to fight with all its might and weapons to kill as many Arabs as it can. Hopefully if all goes well, half the Middle East will be Israeli. Our young have been trained well for the last decade or so on combat console games, it was interesting to see the new Call of Duty Modern Warfare 3 game, which mirrors exactly what is to come in the near future with its predictive programming. Our young, in the US and West, are prepared because they have been programmed to be good soldiers, cannon fodder, and when they will be ordered to go out into the streets and fight those crazy Chins and Russkies, they will obey their orders. Out of the ashes we shall build a new society, there will only be one superpower left, and that one will be the global government that wins. Don't forget, the United States, has the best weapons, we have stuff that no other nation has, and we will introduce those weapons to the world when the time is right."
- http://ec.europa.eu/research/iscp/index.cfm International Cooperation for lasting solutions