The idea of a World Government is pretty old and has already been discussed by many philosophers and politicians.
Theoretical benefits of this concept:
- Humanity would no longer be split
- Worldwide peace & no military needed
- Better wealth, food, and medical distribution
- One economy & currency
To establish this system a global crisis is needed. This could be a world wide economic crash, a great war or a humanitarian disaster. The suffering of people must be high. Media and the current governments need to cooperate to convince the citizen. Otherwise it's impossible to change the system. Only agony makes the people forget their national pride.
What's needed to keep this state ?
One executive, legislature, judiciary and constitution. There will be one main government which consits of representatives of old governments and economy. The administration is divided between several federal states which are subordinated to the main government. The federal states have a limited power to act. They are mainly for law execution and management. The currency system will be renewed and the economy more regulated. There will be more monitoring of citizens to measure the dissatisfaction of the people to avoid riots.
A World Government is possible. The consequences before it is established are particularly bad for the citizen. To keep the system all lose some freedom to obtain long-term peace.
That's not my opinion what should happen. It's just a szenario.