The document that serves as the foundation for the U.S. Constitution is the Articles of Confederation, adopted in 1781. However, it was soon realized that the Articles created a weak federal government, leading to numerous issues, such as lack of centralized control and ineffective governance. This prompted the Constitutional Convention of 1787, resulting in the drafting of the current U.S. Constitution, which established a strong federal framework while balancing power between the states and the national government. The Constitution has since been amended to adapt to changing societal needs and remains the supreme law of the land.