From 1603, the kingdoms of Scotland and England shared the same monarch when James VI of Scotland became James I of England on the death of Elizabeth I.  Across the seventeenth century, the monarchical union was unstable because it was difficult for the shared monarch to balance the needs of the Scottish and English kingdoms.  Anglo-Scottish tensions rose when the Revolution of 1688-9 increased the independence of the Scottish Parliament and reinstated a Presbyterian national church in Scotland while the English church remained Episcopalian.  By 1700 King William II and III was convinced that the regal union wasn’t working.  Both William and his successor Queen Anne pursued an incorporating union but found limited support in Scotland and less in England. The death of Anne’s last child in 1701 created a succession crisis in which an oppositional majority in the Scottish Parliament of 1703-4 refused to accept the English successor to Anne, the Protestant Sophia of Hanover, without union reform.  By 1705 English Whig ministers were prepared to accept incorporation as a means to settle the succession.  The English Alien Act of 1705 threatened economic sanctions if Scotland did not either settle the succession or negotiate a union.  

The resulting treaty proposed that the kingdoms of Scotland and England would unite to create a new kingdom of Great Britain.  It stipulated that the monarch of Great Britain had to be a Protestant and named the Protestant Sophia of Hanover as the heir to Queen Anne.  A new British Parliament would be created with the addition of Scottish representatives to the English Parliament (about 10% of the new total).  Barriers to trade between Scotland and England would be removed and English customs and excise taxes applied across the new British trading zone.  Scottish merchants would be allowed to trade freely with English colonies.  The treaty met with vociferous opposition both inside and outside the parliamentary chamber in Scotland.