Why did the framers include the principles they did in writing the Constitution?Why did the framers include the principles they did in writing the Constitution?
The Articles of Confederation failed because they did not give the central government enough power. It had no power to tax, to raise troops for an army, to control interstate commerce, and to stop states from printing money, among many others. So the framers of the Constitution knew that they had to create a strong federal government, but at the same time make sure it did not become too powerful. So they incorporated the principles of Separation of Powers, Checks and Balances, and Federalism into the Constitution.
The framers of the Constitution (those who framed, or wrote, the Constitution) feared a powerful central, or national, government. In order to keep the national government from becoming too strong, they divided the government into three branches, the legislative, the executive and the judicial. The framers then gave each branch separate, specific powers. This is known as separation of powers—that is, the powers of the national government were divided among the three branches of government.
The framers were also concerned about one branch of government gaining too much power; therefore, they also established a system of checks and balances. Each branch of government was given the ability to check the power of the other two branches of government.
Finally, the framers of the Constitution were concerned that a national government would dominate the state governments—that is, the national government would have too much power and the state governments would have too little power. To keep this from happening, the framers established a government based on federalism. In this system, power would be divided between the federal government (that is, the national government) and the state governments. Some powers would be given or delegated only to the federal government, some powers would be reserved to the states, and some powers would be shared—both the federal government and state governments would have that power.
This sort of depends on which principles you mean, but the major principles of the Constitution were included so as to A) avoid having a central government that was too weak and B) prevent any part of government from having too much power. The Framers wanted a government that was "just right" -- not too strong, not too weak.
Under the Articles of Confederation, the federal government was too weak. The Framers believed to some degree in nationalism and so they wanted to give the national government more power.
At the same time, they believed in limited government. They wanted to prevent the government from being able to do too much, too easily. Because of this, they put in separation of powers and checks and balances, along with some specific prohibitions against things like bills of attainder.
I agree with brettd that much of the Constitution was written in reaction to the colonists' experience with the British monarchical system of government. In particular, the creation of a tripartite system of government, with three roughly equal branches, would theoretically prevent a tyrant from taking control of the country. The checks and balances imposed by the executive, judicial, and legislative branches all work together to ensure that authority is spread widely enough so that no single person or branch can seize control.
Many of the principles they included, separation of power, checks and balances, the freedoms and limits contained in the Bill of Rights, were placed there because of specific experiences we had had at the hands of the British monarchy, and in order to gain enough colony-wide support for a Constitution, people wanted guarantees that similar injustices could not happen under the new government.
I think they included these principles to prevent any one person or family from having too much power and control. As mentioned above most of the checks and balances were put in place to prevent what happened in England from happening here.