In the first principle of nature, self preservation, there is nothing which is repugnant to war; indeed all things rather favour it; for the end of war, the preservation of life and limb, and the retention, or acquisition of things useful to life, agrees entirely with that principle.....Again, Right Reason and the nature of Society .... do not prohibit all force, but that only which is repugnant to Society; that is that which is used to attack the Rights of others.
Hugo Grotius (one generation after Martin Luther), The Law of War and Peace (1625) addressing the subject of lawful relations of the emerging nation states.