The history of the formation of the United Kingdom has involved personal and political union across Great Britain and the wider British Isles. The United Kingdom is the most recent of a number of sovereign states that have been established in Great Britain at different periods in history, in different combinations and under a variety of polities. Norman Davies has counted sixteen different states over the past 2000 years. By the start of the 16th century, the number of states in Great Britain had been reduced to two: the Kingdom of England (which included Wales and controlled Ireland) and the Kingdom of Scotland. The Union of Crowns in 1603, the unintended consequence of a royal marriage 100 years earlier, united the kingdoms in a personal union, though full political union required a Treaty of Union in 1706, Acts of Union in 1707 (to ratify the Treaty), and a further Act of Union in 1800 to include Ireland in the United Kingdom of Great Britain and Ireland.