What is the primary purpose of the Constitution?

The primary purpose of the Constitution is to define the government structure and its powers. This foundational document establishes the framework for the U.S. government, outlining the roles and responsibilities of the legislative, executive, and judicial branches. It delineates the balance of power among these branches to prevent any one branch from becoming too powerful. The Constitution also sets forth the principles of federalism and the relationship between the states and the federal government, ensuring that the rights of both individual states and citizens are protected.

The other options, while they touch on aspects related to governance and law, do not capture the overarching purpose of the Constitution as effectively. Establishing laws for citizens to follow is a function that arises from the Constitution but is not its primary purpose. Similarly, promoting political parties and serving as a historical document are secondary applications of constitutional principles rather than defining the central aim of the document itself. Thus, the focus on structuring government and defining its powers clearly establishes why this answer is the most accurate.