Victor Davis Hanson has an essay over at NRO called Only Deterrence Can Prevent War. He makes the case from history that wars happen when one side thinks that it can beat the other. He makes the further point that wars end when one side becomes convinced that it has been beaten.
Not the League of Nations or the United Nations. Unfortunately, war is a sort of cruel laboratory experiment whose bloodletting determines which party, in fact, was the stronger all along. Once that fact is again recognized, peace usually follows.
Read the whole thing.
As a Viet Nam veteran, I note that the United States could have crushed North Vietnam at will, but that we lacked the will. Strength is more than superior firepower. It has a moral component.