The English purpose was to ensure that Scotland would not choose a monarch different from the one on the English throne. The two countries had shared a king for much of the previous century, but the English were concerned that an independent Scotland with a different king, even if he were a Protestant, might make alliances against England. The English succession was provided for by the English Act of Settlement 1701, which ensured that the monarch of England would be a Protestant member of the House of Hanover. Until the Union of Parliaments, the Scots could choose their own successor to Queen Anne: the Scottish Act of Security 1704 explicitly required a choice different from the English monarch.
Ireland, the third of the "sister kingdoms", was not included in the union. It remained a separate kingdom and indeed was legally subordinate to Great Britain until 1784. Ireland's benefits from the Union of 1707 were few. Its preferential status in trade with England now extended to Scotland. However, Ireland was left unequal and unrepresented in the Parliament of Great Britain. In July 1707 each House of the Parliament of Ireland passed a congratulatory address to Queen Anne, praying that "May God put it in your royal heart to add greater strength and lustre to your crown, by a still more comprehensive Union". The British government did not respond to the invitation and an equal union between Great Britain and Ireland was out of consideration until the 1790s. The union with Ireland finally came about on 1 January 1801.