During the 17th and early 18th centuries, philosophers started to question traditional ideas, such as the belief that kings ruled by divine right. During this period, known as the Age of Enlightenment or the Age of Reason, political thinkers argued humanity could be improved through an exploration of reason and rational dialogue. These theories inspired the American and French Revolutions, and spawned ideas that live on in America's government and institutions.

Locke and Liberalism

John Locke's liberal theories inspired Thomas Jefferson and James Madison, who incorporated those ideas in America's founding documents. Generally, Locke believed a government's authority over its people came from their consent, not from conquest or some natural or divine right. Jefferson drafted the Declaration of Independence using many arguments he'd read in Locke's essays. In particular, Locke urged governments existed based on a metaphorical contract with the people they governed. When the government failed to uphold its end of this contract, the people had the right to revolt against it. Locke's idea that people form governments to protect their God-given rights such as freedom of expression and freedom of religion are embodied in the Constitution's Bill of Rights.

Rousseau's Social Contract

Like Locke, Jean-Jacques Rousseau believed government authority was grounded in a social contract. However, Rousseau's governmental ideal was considerably more democratic than Locke's. According to Rousseau, the only way people could truly be free was in a direct democracy where the people governed themselves. Because representative governments can give rise to factions, allowing each citizen to vote directly on all laws is the only way the government can reflect the true will of the people. Thomas Paine was inspired by Rousseau when he wrote "The Rights of Man," his famous work denouncing Great Britain's abuses of its North American colonists.

Adam Smith and the Free Market

For Locke, the primary purpose of government was the protection of private property. People would only have the freedom to engage in other pursuits if they knew their land and the fruits of their labor were protected. Adam Smith took this idea and went a step further, arguing that aside from protecting people's property, the government should be relatively hands-off in regulating markets and trading. For Smith, free trade enabled people to pursue their own self-interested desire to increase their own property. This pursuit helped supply the wants and needs of the country at large, increasing the wealth of the entire nation. Smith's concepts gave birth to free market capitalism, greatly influencing the structure of the US economy.

Montesquieu and Balance of Power

French political thinker Baron de Montesquieu's "The Spirit of the Laws," published in 1748, became one of the founding texts for modern political theory and greatly influenced James Madison as he drafted the Constitution. Montesquieu was concerned that in large republics governed by representation, factions would form and run the government for their own private interests rather than for the public good. From his perspective, this threat could be eliminated by carefully crafting the branches of government so that each had checks on the others. If no one branch was supreme, Montesquieu reasoned, "ambition counteracts ambition," and no faction would be able to take control. His ideas were the foundation of the US's system of checks and balances.