I have never believed that there is a secret United Nations plot to take over the US. I have never seen black helicopters hovering in the sky above Montana. But, for the first time in my life, I think the formation of some sort of world government is plausible.
A "world government" would involve much more than co-operation between nations. It would be an entity with state-like characteristics, backed by a body of laws. The European Union has already set up a continental government for 27 countries, which could be a model. The EU has a supreme court, a currency, thousands of pages of law, a large civil service and the ability to deploy military force.