The formerly separate kingdoms had been in personal union since James VI of Scotland became King of England and King of Ireland in 1603 following the death of Elizabeth I, bringing about the "Union of the Crowns". Since the reign of James VI and I (), who had been the first to refer to himself as "king of Great Britain", political union between the two mainland British kingdoms had been repeatedly attempted and aborted by both the Parliament of England and the Parliament of Scotland. The reign of Anne () did not produce a clear Protestant heir and endangered the line of succession, with the laws of succession differing in the two kingdoms and threatening a return to the throne of Scotland of the Roman Catholic House of Stuart, exiled in the Glorious Revolution of 1688.