James IV of Scotland married Henry VIII’s sister Margaret Tudor, and in the Reformation Scottish Protestants turned to the Protestant English to oppose the Catholic French.
James VI of Scotland and I of England dreamed of a united kingdom of Great Britain and Scots and English increasingly operated as if they were two parts of one country, especially in religion. The Scots played a vital role in England’s civil wars but when they crowned Charles II in Edinburgh in 1651, Cromwell stormed north and imposed rule from London. England and Scotland were uneasily united until the Restoration in 1660.
In 1688 James VII and II was overthrown in England and the Scots were indignant at not having been involved. They soon hinted that they would crown James’s son rather than accept the Protestant Elector of Hanover the English wanted: that alarmed the English! Meanwhile Scots’ costly scheme to establish a colony at Darien in Panama had completely collapsed, almost bankrupting the country.
They desperately needed access to England’s growing wealth: England wanted to head off a Stuart restoration. The 1707 Act of Union fitted both purposes just nicely.