The mid-seventeenth century European Westphalian state system came out of the prodigious bloodletting of the Thirty Years war and antecedent conflicts between religious protagonists in the twilight of the Holy Roman Empire. But its achievement in mitigating conflict is somewhat exaggerated. In its aftermath, European states continued to fight locally as well as engage in genocidal wars against non-European people, even while their own hinterland enjoyed relative quiescence. It had not stopped them warring with each other over empire and Europe’s relative calm was also shattered by the French revolution and subsequent Napoleonic imperial surge. The relative peace of the nineteenth century ended with the onset of the greatest conflicts of history during the twentieth, the Westphalian peace repudiated by rising German power. The subsequent period of armed peace between the principal international protagonists, after WWII, was due to the accidental constraint imposed by nuclear weapons rather than the balance of power structure, per se, that traces its modern origin to the Westphalian system.