Article Seven of the United States Constitution required nine states to ratify it for the Constitution to take effect.
The rule was a major departure from the Articles of Confederation, which required unanimous approval for amendments. Article Seven instead declared that ratification by conventions in nine states would establish the Constitution among the states approving it.
New Hampshire became the ninth state to ratify, on June 21, 1788. That vote crossed the constitutional threshold, although North Carolina and Rhode Island had not yet joined the new system. The Constitution’s federal government began operating in 1789.
A common mistake is to assume all thirteen states had to ratify before the Constitution could begin. The final two original states joined later: North Carolina ratified in November 1789, and Rhode Island ratified in May 1790. Article Seven’s nine-state formula was therefore central to the transition from the Confederation government.