Constitutionalism

Constitutionalism is a form of political thought and action that seeks to prevent tyranny including worst result of majority rule and to guarantee the liberty and rights of individuals. Constitutionalism is the conduct of politics in accordance with a constitution. 
From the eighteenth century the essential element in modern constitutionalism is the doctrine of limited government under a written fundamental law. 
Limited government means that officials cannot act arbitrarily when they make and enforce public decisions. Public officials cannot simply do as they please. The Constitution is the supreme law that guides and limits the exercise of power by government officials. 
In 1787 representatives of the people of the United States drafted and ratified a Constitution. Article 6 of the United States Constitution states this principle: “The Constitution, and the Laws of the United States which shall be made in Pursuance thereof … shall be the supreme Law of the Land.” All laws, passed either by Congress or by state legislatures, must conform to the supreme law—the Constitution. As Alexander Hamilton explained in the Federalist Papers No. 78: “No legislative act contrary to the Constitution, therefore, can be valid.” Actually, a legislative or executive action that violates the Constitution can be declared unconstitutional, or unlawful, by the Supreme Court.
A constitutional monarchy is a form of government that lies between absolutism and parliamentary republic. In absolutism, the monarch is free to do what he likes, and there is no way to control him. A parliamentary republic operates without a monarch.