But in the night of thick darkness enveloping the earliest antiquity, so remote from ourselves, there shines the eternal and never failing light of a truth beyond all question: that the world of civil society has certainly been made by men, and that its principles are therefore to be found within the modifications of our own human mind. Whoever reflects on this cannot but marvel that the philosophers should have bent all their energies to the study of the world of nature, which, since God made it, He alone knows; and that they should have neglected the study of the world of nations, or civil world, which, since men made it, men could come to know. This aberration was a consequence of that infirmity of the human mind by which, immersed and buried in the body, it naturally inclines to take notice of bodily things, and finds the effort to attend to itself too laborious; just as the bodily eye sees all objects outside itself but needs a mirror to see itself. 

Now since this world of nations has been made by men, let us see in what institutions all men agree and always have agreed. For these institutions will be able to give us the universal and eternal principles (such as every science must have) on which all nations were founded and still preserve themselves. 

Paragraphs 331-332. 

Bergin and Fisch translation