3 main systems of governmental distribution of power
- unitary systems
- confederal systems
- federal systems
The United States, under the Constitution, operates under a model we call dual federalism.
This would, in Madison's mind, be the best way to ensure the protection of liberty and preservation of the nation in his new republic. One of the reasons it would do so is because it would allow the states a certain amount of autonomy. Therefore, various political subcultures would develop in the individual states that was more reflective of the people of that state than of the nation as a whole.
Note what Madison said about this in Federalist No.51. Its in the back of your book. There is also an excerpt on p.90 of the text.
In essence, this autonomy allows the states to serve as 'laboratories of democracy'. Google that term and see what comes up.