The answer is: The separation of powers
The United States Constitution was created in order to provide the necessary checks and balances to keep the powers of the government in check, in doing so it separated said powers into three branches: The Judicial, the Executive and the Legislative.
In separating the different branches of government each would not reign over the order, rather it would serve to check to power among these different branches, granting a balance in power and negating absolute rule in one branch.