System of Checks and Balances
The people of the U.S. created the system of checks and balances, so no one group would have too much power. The Legislative Branch, Executive Branch, and the Judicial Branch all check of each other. For example, if the Executive Branch (president) wants to come up with a law, and the Legislative Branch (congress) wants it too. Then the Judicial Branch (supreme court) says that that is illegal, they can have that law.