But if you think about it a certain way, we already have one world government, the natural laws of the Earth.
In general, all species obey those natural laws of the governing authority of the Earth, except for the species homo sapien.
The meaning of the species description "homo sapien" reveals who thought up that description:
Homo sapiens (Latin: "wise man" or "knowing man"), the only extant member of the Homo genus of bipedal primates in Hominidae, the great ape family. However, in some cases the term is used to refer to any member of the genus Homo ... Humans have a highly developed brain, capable of abstract reasoning, language, introspection, and problem solving.(ibid). Yes, a homo sapien is responsible for the description calling homo sapiens "wise man" with a "highly developed brain ... capable of ... problem solving".
Be that as it may, the government of the Earth is a subset of the governing laws of the cosmos, which state that planets near central stars shall be destroyed by that central star during that star's evolutionary process, therefore, any species who evolve must develop space travel and migrate to a planet with a younger star if they choose to avoid extinction (e.g. Tenets of Ecocosmology).
It is also axiomatic that a species must keep their planet clean enough to keep that species alive until they accomplish competent space travel to a new home world.
Currently homo sapiens are organized into nations that want to do what they want to do, meaning that other nations can butt out of their business.
Sometimes our species sees a need to cooperate for various reasons, so we agree among or between ourselves on various issues, and publicly declare that agreement.
The United Nations is one such attempt to generate a consensus on as many issues as possible between or among nations who are members.
World civilization is both tacit agreement and publicly declared agreement between nations, generally based upon various forms of intercourse between them.
The formalization of a structure is what scares one world government haters, because they feel that it will require giving up something they do not want to give up.
Thus, world civilization in general today is not completely unlike a group of warlords who have their own territories, which you better not enter without permission, or you can expect a fight of some sort.
There is a dichotomy involved in this situation, because homo sapiens do not have the power to overrule the government of the Earth or the cosmos, being limited instead, to obeying or disobeying that government.
It is debatable whether or not homo sapiens can govern ourselves in order to learn to obey the government of the Earth and the cosmos.
I guess the answer to that, like other issues, is blowing in the wind.
A visit to the Dubai, UAE site for a list of businesses of the world, who have presence there, will provide some evidence that the world is fully engaged in international commerce.
Some of that commerce is contrary to the national interests of the countries those companies call home.
Thus, the national interests of nations do not necessarily control the interests of corporations like British Petroleum, Halliburton, or AIG.
In fact the recent record shows that these companies often do great damage to nations.