The major document that outlined the principles of American democracy in 1787 is the United States Constitution. Drafted during the Constitutional Convention, it established the framework for the national government, delineating the powers and responsibilities of the three branches: legislative, executive, and judicial. The Constitution also enshrined essential rights and liberties in its later additions, known as the Bill of Rights. It aimed to create a system of checks and balances to prevent any single branch from becoming too powerful. The Constitution remains a living document, reflecting the foundational ideals of democracy and influencing political systems worldwide.