Reason and Globalism

Political Philosophy is the study of the 'best' Polity, and, for Spinoza, Reason is the source of that idea.  Now, he characterizes the basic political unit as a 'Commonwealth', by which he seems to mean 'Nation', in contrast with the 'City' of the ancient version of the genre.  Furthermore, he proposes that the best mode of interaction between Commonwealths is that governed by a peace treaty.  However, he does not explain by what authority any such pact can be overseen, a shortcoming indicative of a more fundamental inadequacy in his presentation.  For, insofar as Reason is common to all humans, the best Polity according to it can be only single and global, the internal relations of which are mediated by laws, not by treaties.  Since terms such as 'international' and 'United Nations' presuppose the priority of the Nation as the basic political unit, for want of a better term, the Rational political ideal can be called 'Globalism'.