Two institutions might have thwarted or retarded the development of international law: one was the Catholic Church with its international organization and its claim to universal spiritual supremacy; the other was the Holy Roman Empire, with its claim to temporal predominance and with its insistence upon the essential inequality between itself and all other states. But the Protestant Revolt in the sixteenth century dealt a severe blow to the claim and power of the Catholic Church. And the long struggle between Bourbons and Habsburgs, culminating in the Thirty Years' War, reduced the Holy Roman Empire to a position, in theory as well as in fact, certainly no higher than that of the national monarchies of France, England, and Spain, or that of the Dutch Republic. From the treaties of Westphalia emerged a real state-system in Europe, based on the theory of the essential equality of independent sovereign states, though admitting of the fact that there were Great Powers. Henceforth the public law of Europe was to be made by diplomats and by congresses of ambassadors. Westphalia pointed the new path. Another aspect of international relations was emphasized in the first half of the seventeenth century. It was the Thirty Years' War, with its revolting cruelty, which brought out the contrast between the more humane practice of war as an art in Italy and the savagery which disgraced the Germanies. The brutality of the struggle turned thinkers' attention to the need of formulating rules for the protection of non- combatants in time of war, the treatment of the sick and wounded, the prohibition of wanton pillage and other horrors which shocked the awakening conscience of seventeenth-century Europe. It was the starting-point of the publication of treatises on international law. [Sidenote: Grotius] The first effective work, the one which was destined long to influence sovereigns and diplomats, was Grotius's _On the Law of War and Peace_. Hugo Grotius (1583-1645) [Footnote: Known in his native country as Huig van Groot. The last years of his life he spent as ambassador of Sweden at the French court.] was a learned Dutch humanist, whose active participation in politics against the stadholder of the Netherlands and whose strong protests for religious toleration against the dominant orthodox Calvinists of his country combined to bring upon himself a sentence of life imprisonment. Immured in a Dutch fortress in 1619, he managed to escape and fled to Paris, where he prepared and in 1625 published his immortal work. _On the Law of War and Peace_ is an exhaustive and masterly text-book--the first and one of the best of the systematic treatises on the fundamental principles of international law. ADDITIONAL READING