I mean, sure, if you want a toothless world government with no power that wouldn't be able to keep countries in line. In which case I'm happy to report we already have this: its called the UN.

For anything else you would call an actual government, the highest body has the power and physical force to keep those under them inline. Even in the USA, where states rights are a thing, the federal government could easily force them to do basically whatever they want.

Huge countries like India, the US, and Russia have come under the thrall of men whose position in the feature space is near words like “deranged” and “terrifying”... there’s no reason to believe that the same thing could not happen to a world government