As an altruistic form of international action the principle of intervention has been of slow growth. It required an atmosphere of toleration on a wide scale, and, before this atmosphere could be created, Christian States had to learn toleration for themselves by a hard experience of its necessity. They had, in the first place, to secure toleration for their own nationals and the converts of their Churches in heathen countries where the people could not be coerced or lectured with impunity. In the next place they had to achieve toleration among themselves. Toleration among the Christian Churches--the so-called peace of Christendom--became necessary owing to the struggle between the Reformation and the Counter-Reformation; but it took the Thirty Years' War to prove its necessity. The proof is embodied for all time in the Peace of Westphalia--chiefly in the Treaty of Osnabruck, which was signed in 1648, at the same time as the famous Treaty of Münster. The ostensible effect of the Peace of Westphalia was to place Roman Catholicism and Protestantism on an equal legal footing throughout Europe. A secondary effect was to give a very marked stimulus to the cause of Religious Liberty generally. We may recognise its first fruits in, among other things, the campaign for unrestricted religious toleration during the Commonwealth in England, and its application to the Jews.[2] It was not until 1814 that this principle was extended by Treaty beyond the pale of Christendom. This was in the Protocol of the four allied Powers--Great Britain, Russia, Prussia, and Austria--by which the union of Belgium with Holland was recognised. The return of the House of Orange to the Netherlands after the fall of Napoleon had entailed the promulgation of a new Constitution, which, in view of the democratic traditions of the French occupation, was necessarily of a liberal type. Among its concessions was an article granting the fullest religious liberty. When the Powers were called upon to sanction the union with Belgium, they did so on condition that the new Constitution should be applied to the whole country, and, in view of the religious differences prevailing, emphasised the article on Religious Liberty. This is the form in which it appears in the Protocol:-- * * * * * Art. I.--Cette réunion devra être entière et complète, de façon que les 2 Pays ne forment qu'un seul et même État régi par la Constitution déjà établie en Hollande, et qui sera modifiée, d'un commun accord, d'après les nouvelles circonstances. Art. II.--Il ne sera rien innové aux Articles de cette Constitution qui assurent à tous les Cultes une protection et une faveur égales, et garantissent l'admission de tous les Citoyens, quelle que soit leur croyance réligieuse, aux emplois et offices publics. * * * * *