The purpose of diplomacy is to achieve national goals in the international field. Wars happen when two nations have incompatible goals and diplomacy isn't able

The purpose of diplomacy is to achieve national goals in the international field. Wars happen when two nations have incompatible goals and diplomacy isn't able to resolve them. The wars are fought to achieve national goals, or change the other nation's goals. Diplomacy is ultimately what resolves wars by making the new national goals compatible. Every single treaty or armistice ending a war is a result of diplomacy, even unconditional surrenders.