Answer: In the Constitution of the United States.
The Constitution establishes the basic rules and structure of a strong federal government with three branches (Executive, legislative and Judicial) along with a system of check and balance to oversees and to limit each other's powers. It provides outlines in which each branch shall be composed, their main duties, how their members shall be elected and their limitations. Besides this, the Constitution also provides fundamental laws to guarantee certain rights of its citizen such as the right to life, freedom, privacy, democracy, among others.
