In September 1815 Tsar Alexander (who was still under the influence of Julie von Krüdener), Francis I and Frederick William III (and all European rulers except the pope, the sultan and the Prince Regent) signed a Holy Alliance (the countries depicted right) to deal with each other and other peoples on the basis of Christianity. The pragmatic Castlereagh described it as
‘a piece of sublime mysticism and nonsense’.A more realistic treaty was signed in November – the Quadruple Alliance Treaty. This set up the ‘Concert of Europe’ by which Britain, Russia, Austria, Prussia attempted to control events by regular consultation (summit conferences) among themselves. This is known as the Congress System.
At the Congress of Aix-la-Chapelle in 1818 the French indemnity was revised, the occupation was ended and France was invited to join the Concert of Europe.
From this point the Congress System became a weapon for the conservative monarchies to stamp out revolutionary movements. Successive congresses were held at Troppau (1820) and Laibach (Ljubljana) (1821) to address the problems of revolution in Spain and Italy. Metternich urged that the system take concerted action against these movements but the British stood aside.
At the Congress of Verona in October 1822 the question of allied intervention in the Spanish and Greek revolutions was strongly opposed by Britain (represented by Wellington after Castlereagh’s suicide in August). Metternich was caught between his desire to maintain friendly relations with Britain and his inclination to suppress revolutionary movements. This meant there could be no common allied purpose. In 1823 French troops unilaterally invaded Spain to defeat the republicans and restore the monarchy.
And here's a trivial pursuits point. On 31 August 1823 French forces led by the Duc d'Angoulême, son of the future king, Charles X, captured the island of Trocadero inside the Bay of Cadiz, in the south of Spain, bordering the Spanish mainland.
The French intervention in effect marked the end of the Congress System and confirmed Britain's isolation in Europe.