The legal document that provided the foundation for the American system of governance is the U.S. Constitution, ratified in 1788. The Constitution established the structure of the federal government, delineated the separation of powers among the legislative, executive, and judicial branches, and outlined the rights of citizens. It also included mechanisms for amending the document, reflecting the founders' recognition of the necessity for adaptability over time. The Constitution served as a guiding framework for governance, embodying principles of democracy and rule of law that continue to influence political discourse and practice in the United States today.