The idea that “perpetual peace” is possible in a nation which is guided by reason and science is one of the great political myths to come out of the Age of Enlightenment. Perpetual peace is an unrealizable concept, because national politics (like the tribal conflicts of the prehistoric times) has always been and always will be: Civil War.
The use of political violence is the “natural” method of achieving political objectives. Mankind is incapable of creating a nation in which every political faction voluntarily adopts the peaceful methods of politicking. The breaking of one chain of political violence, leads to the start of another chain. When old conflicts end, they make space for new ones, and a new cycle of political violence commences. Through the contest of antagonistic political forces, the nation keeps transforming itself, it becomes better or worse, it rises to greater heights or declines and falls. A nation can never be free of political violence, but it can try to prevent such violence from getting out of control, by deploying counter-political violence through law enforcement agencies (such strategies are effective in creating a semblance of peace in the short-term but never perpetually).
The price for short-term political peace is frightfully high—heavy financial and psychological investment must be made for creating a system of rule of law which cannot be corrupted by the forces which are battling for political power. In the words of Vegetius, the Roman General, only those nations which prepare for war, can attain peace.