The Holy Alliance had not as such any importance for International Law, for it was a religious, moral, and political, but scarcely a legal alliance. But at the Congress of Aix-la-Chapelle in 1818, which the Emperors of Russia and Austria and the King of Prussia attended in person, and where it might be said that the principles of the Holy Alliance were practically applied, the Great Powers signed a Declaration,[43] in which they solemnly recognised the Law of Nations as the basis of all international relations, and in which they pledged themselves for all the future to act according to its rules. The leading principle of their politics was that of legitimacy,[44] as they endeavoured to preserve everywhere the old dynasties and to protect the sovereigns of the different countries against revolutionary movements of their subjects. This led, in fact, to a dangerous neglect of the principles of International Law regarding intervention. The Great Powers, with the exception of England, intervened constantly with the domestic affairs of the minor States in the interest of the legitimate dynasties and of an anti-liberal legislation. The Congresses at Troppau, 1820, Laibach, 1821, Verona, 1822, occupied themselves with a deliberation on such interventions.
[43] See Martens, N.R. IV. p. 560.
[44] See Brockhaus, "Das Legitimitätsprincip" (1868).
The famous Monroe Doctrine (see below, § [139]) owes its origin to that dangerous policy of the European Powers as regards intervention, although this doctrine embraces other points besides intervention. As from 1810 onwards the Spanish colonies in South America were falling off from the mother country and declaring their independence, and as Spain was, after the Vienna Congress, thinking of reconquering these States with the help of other Powers who upheld the principle of legitimacy, President Monroe delivered his message on December 2, 1823, which pointed out amongst other things, that the United States could not allow the interference of a European Power with the States of the American continent.
Different from the intervention of the Powers of the Holy Alliance in the interest of legitimacy were the two interventions in the interest of Greece and Belgium. England, France, and Russia intervened in 1827 in the struggle of Turkey with the Greeks, an intervention which led finally in 1830 to the independence of Greece. And the Great Powers of the time, namely, England, Austria, France, Prussia, and Russia, invited by the provisional Belgian Government, intervened in 1830 in the struggle of the Dutch with the Belgians and secured the formation of a separate Kingdom of Belgium.
It may be maintained that the establishment of Greece and Belgium inferred the breakdown of the Holy Alliance. But it was not till the year 1848 that this alliance was totally swept away through the disappearance of absolutism and the victory of the constitutional system in most States of Europe. Shortly afterwards, in 1852, Napoleon III., who adopted the principle of nationality,[45] became Emperor of France. Since he exercised preponderant influence in Europe, one may say that this principle of nationality superseded in European politics the principle of legitimacy.
[45] See Bulmerincq, "Praxis, Theorie und Codification des Völkerrechts" (1874), pp. 53-70.
The last event of this period is the Crimean War, which led to the Peace as well as to the Declaration of Paris in 1856. This war broke out in 1853 between Russia and Turkey. In 1854, England, France, and Sardinia joined Turkey, but the war continued nevertheless for another two years. Finally, however, Russia was defeated, a Congress assembled at Paris, where England, France, Austria, Russia, Sardinia, Turkey, and eventually Prussia, were represented, and peace was concluded in March 1856. In the Peace Treaty, Turkey is expressly received as a member into the Family of Nations. Of greater importance, however, is the celebrated Declaration of Paris regarding maritime International Law which was signed on April 16, 1856, by the delegates of the Powers that had taken part in the Congress. This declaration abolished privateering, recognised the rules that enemy goods on neutral vessels and that neutral goods on enemy vessels cannot be confiscated, and stipulated that a blockade in order to be binding must be effective. Together with the fact that at the end of the first quarter of the nineteenth century the principle of the freedom of the high seas[46] became universally recognised, the Declaration of Paris is a prominent landmark in the progress of the Law of Nations. The Powers that had not been represented at the Congress of Paris were invited to sign the Declaration afterwards, and the majority of the members of the Family of Nations did sign it before the end of the year 1856. The few States, such as the United States of America, Spain, Mexico, and others, which did not then sign,[47] have in practice since 1856 not acted in opposition to the Declaration, and one may therefore, perhaps, maintain that the Declaration of Paris has already become or will soon become universal International Law through custom. Spain and Mexico, however, signed the Declaration in 1907, as Japan had already done in 1886.
[47] It should be mentioned that the United States did not sign the Declaration of Paris because it did not go far enough, and did not interdict capture of private enemy vessels.