Perhaps there is a "world government" that is but the combined Territorial Government of all U.N. Members? A treaty entered into by a
low contracting party would only bind it territorially but not 'organically'. The sovereign members of a confederation would remain unaffected by the treaties of the confederation though those treaties might be binding upon the territories thereof--unless the sovereign members ratified such treaties. For example Agend21 and other UN Treaties to knowledge might only apply within the territories of the United States. In 'international law' parties to treaties are expected to know and be aware of the internal mechanisms of the other parties to a treaty.