Article Seven required nine states to ratify the U.S. Constitution for it to take effect.
This threshold represented a compromise between requiring unanimous approval and allowing a small minority of states to establish the new government. The Constitution was submitted to state conventions in September 1787, after the Constitutional Convention completed its work in Philadelphia.
New Hampshire became the ninth state to ratify, on June 21, 1788. That vote made the Constitution operative among the ratifying states, although the first federal government under the new document began functioning in 1789.
The remaining four original states ratified later. North Carolina approved the Constitution in November 1789, while Rhode Island held out until May 29, 1790. The distinction between the nine-state threshold and unanimous approval is an important difference between the Constitution and the Articles of Confederation.