At the time that the Constitution was written, nine of the 13 states were required for ratification. It took 10 months and a vigorous campaign by proponents of the document to get the first nine states to approve the Constitution.
The supporters of the Constitution included James Madison, Alexander Hamilton and John Jay. These three men penned a series of essays that were compiled into a book called "The Federalist," which was a response to anti-federalist complaints. The essays detailed the different parts of the Constitution as well as the reason why things were stated the way they were. These efforts, as well as the addition of the Bill of Rights, were the main contributing factors leading to the ratification of the Constitution.