One purpose of the U. S. Constitution was to

The Constitution of the United States established America's national government and fundamental laws, and guaranteed certain basic rights for its citizens

Explanation: First it creates a national government consisting of a legislative, an executive, and a judicial branch, with a system of checks and balances among the three branches. Second, it divides power between the federal government and the states. And third, it protects various individual liberties of American citizens.