What document establishes the basic principle of civilian control of the US Armed Forces?

The U.S. Constitution is the foundational document that establishes the principle of civilian control of the military. This principle is rooted in the Constitution's framework, which designates the President as the Commander-in-Chief of the Armed Forces, while Congress holds the power to declare war and regulate the military. This structure ensures that elected civilian leaders maintain authority over military operations, thereby reinforcing the democratic principle that the military is subordinate to civilian governance.

The Constitution also establishes checks and balances through the separation of powers, where different branches of government oversee different aspects of governance, including the military. This prevents any single entity from becoming overly powerful and ensures that military decisions reflect the will of the civilian populace.

In contrast, documents like the Bill of Rights specifically address individual rights and freedoms, and the Declaration of Independence focuses on the reasons for the colonies' separation from Britain. The National Defense Authorization Act, while it does deal with military funding and policy, does not establish the constitutional principle of civilian control but rather operates within the framework already set by the Constitution. Thus, the U.S. Constitution is fundamental in establishing the principle of civilian control over the military.