The United States Constitution was ratified on June 21, 1788, when New Hampshire became the ninth state to endorse it. This ratification was a pivotal moment in U.S. history, establishing the framework for the federal government. The Constitution replaced the Articles of Confederation, addressing significant weaknesses in governance, such as federal authority and interstate relations. Its ratification marked the beginning of a new political era based on democratic principles, checks and balances, and the protection of individual rights. The document has since been amended and interpreted, guiding American political life through centuries of change.