Ok, here is a succinct explanation. I have a MENSA certified 150 IQ and I am pretty sure I am the smartest person on /pol/, so pay attention.
1. There is ABSOLUTELY NOTHING WRONG with world government/globalization/etc.
2. It has to be a natural process that would likely take many hundreds of years where humanity becomes one, but different regions preserve a legacy of their heritage throughout the ages, albeit joined into a common world.
3. You cannot force it, like the EU and UN are trying to do, because it breeds resentment, aggression and opposition.
...and a very important point...
4. You ABSOLUTELY CANNOT do it with incompatible cultures. Muslims/Arabs can never be a part of the same culture as Christians/Europeans. The cultures must be able to co-exist and work together seamlessly.
5. There has not been even one successful multicultural society in history, NOT EVEN ONE, and I have two fucking degrees in history, so don't even try to argue this with bullshit wiki links you just googled.>"but USA is a successful multi..."
6. Nope, you are just a brainlet. It actually proves my point. The USA was formed by one culture - white, Christian, Western European. The settlers spoke Latin derived languages, had the same religion, had mostly the same customs, habits, attitudes, views, etc. The problem started when a foreign and incompatible culture - nigger slaves - were mixed in and freed.
7. tl;dr (but you should really read it, because I am smarter than you and you will learn something): a world government works only as a natural process, voluntary, spanning a long stretch of time that includes only compatible cultures.