Which foundational document emphasizes government by the people and separation of powers?

The U.S. Constitution is the foundational document that emphasizes the principles of government by the people and the separation of powers. It establishes a framework for the government and outlines how power is distributed among three distinct branches: the legislative, executive, and judicial. This separation is crucial because it prevents any one branch from becoming too powerful, ensuring a system of checks and balances where each branch can oversee and limit the actions of the others.

Additionally, the Constitution highlights the concept of popular sovereignty, which asserts that the government's authority comes from the consent of the governed. This principle is reflected in the preamble, which begins with "We the People," emphasizing that the ultimate power resides with the citizens of the nation.

In contrast, other documents such as the Magna Carta are focused on limiting the powers of the monarchy and establishing certain legal rights, while the Declaration of Independence articulates the reasons for separation from British rule but doesn't provide a structure for governance. The Bill of Rights, although vital for protecting individual liberties, serves as an amendment to the Constitution rather than outlining the overarching governmental structure itself.