The Constitution of the United States is traditionally divided into three parts: the preamble, the seven articles, and the twenty-seven ratified amendments. Another division is possible between the first ten amendments, collectively called the Bill of Rights, and the following seventeen. The amendments in the Bill of Rights were drafted together in 1789 and ratified together, after more than two years of intense debate, in 1791.
The three main parts of the Constitution are strikingly different in length, with the one-sentence Preamble being by far the briefest:
We the People of the United States, in Order to form a more perfect Union, establish Justice, insure domestic Tranquility, provide for the common defence, promote the general Welfare, and secure the Blessings of Liberty to ourselves and our Posterity, do ordain and establish this Constitution for the United States of America.
To modern readers, the preamble to the Constitution might seem like a mere formality. However, this single sentence is vital for two principal reasons. First, it was by no means a matter of course to have a national constitution at all. The Constitution of the United States is the oldest written constitution still in force and has served as a model for other countries which have adopted similar legal frameworks. The mother country, Great Britain, does not have a written constitution, though it does have a Bill of Rights, on which the United States Bill of Rights is partly based.
In the second place, the preamble established a vital principle with the first three words. The ultimate authority behind the Constitution was not to be Congress or the president, but "We the People." While the Declaration of Independence separates the new republic from what it describes as the tyranny of the British government, the Constitution is largely devoted to the precise description and limitation of the powers of the new American government, to ensure that it does not become equally tyrannical.