The historical document that lays the foundation for the structure of the U.S. government is the Constitution of the United States. Drafted in 1787 and ratified in 1788, the Constitution established the framework for federal governance, delineating the powers of the three branches: executive, legislative, and judicial. It incorporates principles such as checks and balances, federalism, and the separation of powers to prevent any one branch from becoming too powerful. Additionally, the Bill of Rights, the first ten amendments added in 1791, guarantees individual liberties and civil rights, emphasizing the importance of safeguarding personal freedoms within the government framework.