The Road to WWI from Congress of Vienna (1815-1914):
In 1815 Napoleon Bonaparte was defeated for the last time in Belgium at waterloo. The Battle of Waterloo was his last battle. Then the European head of states come together at Vienna and resettled the disputed map of Europe, created by Napoleon. The Congress of Vienna paved the way to a collective system in which almost every nation of Europe was represented. In other words an early version of the United Nations. The year between 1815 to 1914 was disturbed by two events. First, the Russian attempt to control Constantinople and the strait of Dardanelles which leads to the Crimean war of 1854-1856. Britain and France helped Ottoman Empire and the Russian advancement was stopped. Overall this event does not disturb the balance of power in Europe. But it did help Bismarck in his diplomacy against France. This prevents the Franco-Russian alliance against the rising Prussia and German confederate.
Bismarck's 'Blood and Iron' policy make it possible to make a unified Germany. The Franco-Prussian war of 1870-71 replaced France with Germany as a European power. This war make France weak but they were able to keep the balance of power for some time. The German Empire was proclaimed at Versailles. A similar event took place in Italy under the leadership of Count Cavour which created a unified Italy. This decline of France and Austria led to the rise of two major power in the European state systems, Germany and Italy.
The Ottoman Empire's strength delined in the Balkan added more states to the European state Systems. Greece, Serbia, Romania, Albania, and Bulgaria become independent.
America with its expansion policy and war with Spain (Spanish-American war in 1898) gain more territory and also bought Alaska for $7.2 million dollars in 1867. After the Crimean war Russia was in short of cash because of the war and fear that in the future war with Britain, they might take it by force of arms. So they sold it to a more neutral power toward Russia, America. Some countries in South America gain independence during Napoleonic War. Brazil gain its independence in 1882 from Portugal.
In the far east the rise of japan surprised the European Nations. The victory over China in 1894-95 increased its spear of influnce. Britain make an alliance with Japan in 1902. The Russian Tsar seeks a decisive victory for popularity at home so he chooses Japan as his adversary. But Japan turn it into a glorious victory over Russia in 1904-05. She was regarded and granted a major Power status of the World. Japan's interest was limited to the far east, she did not add much to the European balance of power.
Germany, Italy, and Austria formed an Alliance in 1882 which is known as the 'Triple Alliance'. The purpose of the alliance was to keep the status quo of 1871 (Germany defeat France). A sort of polarization took place and as a countermove, Britain, France, and Russia team together formed 'Triple Entente' in 1905. The planarization created by Alliance and counter Alliance was one of the causes of World War I. World War I dismantled the German Empire, Austro-Hungarian, Ottoman Empire, and the tsarist Russia which will become the Soviet Union.
Between 1815 to 1914 there was a relative peace which is sometimes referred to as Pax Britannica (British Peace). During this period Britain was the hegemonic power but in Europe, they used it for balance, the balance of power between European Power.