Since every nation tends to believe that each of its past wars was fought in self-defence, a drawn war is more likely to be remembered as a victory.

When two nations had a contradictory assessment of their own military power and the issue at state was vital to both nations, war was likely.

Wars end when nations agree that war is an unsatisfactory instrument for solving their dispute; wars begin when nations agree that peaceful diplomacy is an unsatisfactory instrument for solving their dispute. Agreement is the essence of the transition from peace to war and from war to peace, for those are merely alternating phases of a relationship between nations.

Manchester’s disciples believed that paradise was an international bazaar. They favoured the international flow of goods and ideas and the creation of institutions that channeled that flow and the abolition of institutions that blocked it. Nations, they argued, now grow richer though commerce than though conquest.

In the palace of glass and iron, the locomotive and telegraphic equipment were admired not only as mechanical wonders; they were also messengers of peace and instruments of unity.

Why did nations turn so often to war in the belief that it was a sharp and quick instrument for shaping international affairs when again and again the instrument had proved to be blunt or unpredictable? This recurring optimism is a vital prelude to war. Anything which increases the optimism is a cause of war. Anything which dampens that optimism is a cause of peace.