Before 1707, Scotland and England were separate nation states, going about their own business. It's true that slightly over 100 years earlier, in 1603, Scotland and England shared Scotland's king, James VI (Mary, Queen of Scots' son) but there was no real desire for a political union.
The reasons for the union of Scotland and England aren't simple, but it's fair to say that after the Darien adventure, in which many Scottish nobles and merchants lost a considerable amount of money, the English saw an opportunity to bind Scotland and remove a potential ally of their enemies.
The screws were tightened in 1705 when England passed the Alien Act. This treated Scots living in England as aliens, authorised the seizing of Scottish property in England and barred Scottish imports. By 1706, it was almost all over.
The Scottish negotiators were mostly pro-union men, appointed by the English queen Anne, and many were bribed to vote in favour to offset their losses from Darien (the failure of which was caused partly by the English) and in 1707 the parliament voted to end Scotland's independence. Scotland and England had joined in a union with its parliament in London, which has remained much the same to this day.
It's worth noting though, that in 1707 there was no representation for the people in the parliament and when they heard what had happened they rioted in the streets, while the lords who had negotiated the union were richly rewarded. Here's an excerpt from the memoirs of Sir John Clerk of Penicuik on the lot of Scotland's representatives to the first sitting of the new British parliament in October 1707:
To find themselves obscure and unhonoured in the crowd of English society, where they were despised for their poverty, ridiculed for their speech, sneered at for their manners, and ignored in spite of their votes by the ministers and government.
Things have surely changed today, haven't they? But if history's your thing, give a moment's thought to the Scots of 1707 who had their independence taken from them, when you vote in a free referendum of 2014 to return it.
Education Scotland: The Treaty of Union, 1689 - 1740
Michael Lynch: Scotland: A New History (Pimlico)
Magnus Magnusson: Scotland: The Story of a Nation (Harper Collins)
Scott Minto: Skintland, Darien and the mythology of the BritNats