The key historical document that established the principles of American government is the Constitution of the United States. Drafted in 1787, it created a framework for government and outlined the separation of powers among the legislative, executive, and judicial branches. The Constitution also includes the Bill of Rights, which guarantees individual liberties and civil rights. It reflects Enlightenment ideals of governance, including principles of democracy, checks and balances, and federalism. This foundational document has been instrumental in shaping the U.S. legal system and continues to influence democratic governance worldwide, serving as a model for other nations.