Article Seven required nine state ratifications before the U.S. Constitution could take effect. This threshold was two-thirds of the thirteen states that existed during the founding era commemorated by America250.
The rule represented a compromise between supporters of a stronger federal government and those who feared that a small number of states could impose a new national system. The Constitution therefore did not require unanimous approval from all thirteen states.
Delaware was first to ratify, on December 7, 1787. New Hampshire became the ninth state on June 21, 1788, and that ratification placed the Constitution into effect. The remaining states still had to decide whether to join the new constitutional system.
Rhode Island was the thirteenth and final original state to ratify, on May 29, 1790. The nine-state rule is distinct from the later amendment process, which generally requires approval by three-fourths of the states.