In which document were the foundational principles of the U.S. government first articulated?

The foundational principles of the U.S. government were first articulated in The Constitution. This document formally established the structure of the government and outlined the separation of powers among the executive, legislative, and judicial branches. It serves as the supreme law of the land and lays down the framework for governance in the United States.

While other documents like The Declaration of Independence set the stage for independence and outline philosophical justifications for governance based on the consent of the governed and natural rights, the Constitution is where the specific mechanisms of government were created and defined. The Federalist Papers offered insights and justifications for the Constitution's principles and provisions but were written after the Constitution to promote its ratification. The Articles of Confederation were the first governing document and established a confederation of sovereign states but were ultimately replaced because they did not provide a strong enough central authority.

Thus, the Constitution is key as it not only encapsulates the foundational principles but also operationalizes them in a way that governs the country.