Answer:
The U.S. Constitution was inspired by the enlightment ideas of John Locke, Montesquieu, among others. From John Locke, it took the idea that government should exist to protect the natural rights of people: life, liberty, and property. The protection of these rights is codified under the Bill of Rights.
Montesquieu thought that government power should be divided in three branches: the executive branch, the legislative branch, and the judicial branch. The U.S. Constitution applied this system and included a series of checks and balances to prevent any of the three branches from becoming too powerful. Finally, the Founding Fathers made America a federal country with a federal system, because the American colonies had previously enjoyed a lot of independence, and they did not want to lose it.