The United Kingdom of Great Britain is a nation in Western Europe, based on the island of Great Britain that was established on April 12, 1922 after the signing of the Anglo-Irish Treaty of 1922. The Treaty required Britain to recognize Ireland's independence and also required Britain to rewrite its Constitution to phase out Ireland. More popularly known as Great Britain, the United Kingdom, or simply just Britain, it now solely exists on the island of Great Britain. Britain is a constitutional monarchy, with its head of government being approved by its head of state after nomination by Britain's House of Commons, which serves alongside the House of Lords in the British Parliament. The Head of State of Great Britain is the British Monarch, currently Queen Elizabeth II, and its Head of Government, proposed by the ruling party in the British House of Commons, the country's lower house of Parliament, and approved by the serving monarch. The country was once the premier superpower of the world, but fell out of place due to its loss to Germany and the Central Powers in World War I. The center of Britain's financial, political, and social influence is in London, the nation's capital, which house Westminster Abbey, the house of the British Parliament.