One world government?

[Anomalocaris]

Or how would it NOT work? What flaws would a one world government have?

the greatest failing of a single world government is it would have little or no incentive to carry out multiple simultaneous experiments in different forms of government as Is carried out on earth today with different political and economic systems is autonomous nation states. As a result the world government would have poor capabilities in assess how changing social outlook, demographics, technology, economic structure and so forth should effect how how it governs. Such a government would likely fall increasingly upon founding documents, rigid principles, ideological dogma, and traditional ways of doing things to justify itself because it would lack clear experimental guidance on how it should change to best lead a changing world.

A world government may well come close to being founded upon the governmental wisdom of humanity as these have accumulated up to the moment of the world government's founding. As a result it well work reasonably well at the beginning and better than majority of the national governments it supplanted, and thus become instrumental in securing a period of unusual prosperity, stability and progress after its founding. But eventually its own monolithic nature would prevent it from adapting to the progress which it may itself have facilitated or promoted, or which may have happened out of its control, and it would become increasingly a burden to greater and greater segments of the population and economy.m

So you might say a world government can give humanity a lot, by extracting all the golden eggs that are in the goose at the moment the world government killed the goose.