The document that established the framework for the United States government is the United States Constitution, adopted in 1787. The Constitution created a system of federal government with three branches: legislative, executive, and judicial, to prevent the concentration of power and ensure a system of checks and balances. It also outlines the rights of citizens and the governing principles of the nation. Initially ratified by thirteen states, the Constitution has since been amended several times to address changing societal needs and rights, including the Bill of Rights, which safeguards individual liberties and freedoms.