The United Kingdom of Great Britain and Ireland was a sovereign state in Northwestern Europe that comprised the entirety of the British Isles between 1801 and 1922. It was established by the Acts of Union 1800, which merged the Kingdom of Great Britain and the Kingdom of Ireland into a unified state. The establishment of the Irish Free State in 1922 led to the remainder later being renamed the United Kingdom of Great Britain and Northern Ireland in 1927.
The United Kingdom, having financed the European coalition that defeated France during the Napoleonic Wars, developed a large Royal Navy that enabled the British Empire to become the foremost world power for the next century. For nearly a century from the final defeat of Napoleon following the Battle of Waterloo to the outbreak of World War I, Britain was almost continuously at peace with Great Powers. The most notable exception was the Crimean War with the Russian Empire, in which actual hostilities were relatively limited. However