The correct answer is: Separation of powers.
This is a political doctrine that refers to the division of the government in the legislative, executive, and judicial functions. They are each in a separate and independent body. In this way, the limitation of arbitrary excesses by government is seeked as the sanctions of all these three branches is needed for making, excecuting, and administering the laws.
This idea was explicitly established by Montesquieu in The Spirit of the Laws written in 1748.
