Back in Europe, after finally defeating Napoleon in 1815 following a series of masssive wars, Austria, Prussia, Russia, Britain set up the first modern system of collective security to contain France, maintain stability and restore the monarchies that Napoleon had overthrown. Under the Treaty of Vienna, the countries in the so-called Concert of Europe agreed to help each other in wars and to suppress internal unrest. They met regularly to settle disputes. The result was 99 years of relative peace among the major European powers. However, they continued to carry out colonial wars. Britain averaged one a year under Queen Victoria.
In this period, Belgium became independent after the Concert powers brokered a peace. Greece was recognized as independent in 1826 after naval intervention by the Concert Powers against the Turkish Ottoman Empire. In France, Louis Philippe overthrew Louis XVIII peacefully.
In addition, the Treaty of Vienna formalized rules of international law, including diplomatic immunity. In the modern era, the Concert of Europe was the first international security organization. For instance, as conservative monarchists, they worked together to crush the liberal democratic revolts of 1848
The one conspicuous failure of the Concert was the bloody Crimean War (1853-1856) between Russia and Britain.