A NATION or a state is, as has been said at the beginning of this work, a body politic, or a society of men united together for the purpose of promoting their mutual safety and advantage by their combined strength.
From the very design that induces a number of men to form a society which has its common interests, and which is to act in concert, it is necessary that there should be established a
Public Authority, to order and direct what is to be done by each in relation to the end of the association. This political authority is the Sovereignty; and he or they who are invested with it are the Sovereign.
http://www.constitution.org/vattel/vattel_01.htm