The significant political document adopted in 1787 in the United States is the U.S. Constitution. This foundational legal framework established the nation's government system and principles, including the separation of powers among the legislative, executive, and judicial branches. The Constitution was drafted during the Philadelphia Convention and aimed to address the inefficiencies of the Articles of Confederation. It also provided a mechanism for amendments, allowing for adaptability over time. The ratification of the Constitution by the states marked a crucial moment in American history, as it created a stronger federal government and has served as a model for democratic governance worldwide.