The French and American Revolutions each had an Enlightenment philosopher that was essential to the philosophical inspiration of each with a specific tract that effectively forms a thesis as to the purpose or reason of their Revolution.

The American Revolution was inspired by John Locke's Second Treatise on Civil Government, a "conservative" (and I put it in quotes because it is liberal to the time period but conservative in comparison to the next philosopher I aim to discuss) work aimed at arguing that government is meant to protect the citizen and their property, "The great and chief end therefore, of Mens uniting into Commonwealths, and putting themselves under Government, is the Preservation of their Property." With a focus on the protection of the citizen's liberty and more importantly, the protection of private property and the transfer of public property to private property through labor of property (as in, it's more useful to a nation that a parcel of land be tilled and cultivated by a private individual for their own benefit than being left alone by the government as public property). The American Revolution is a moderate revolution meant to protect the rights of property and the citizen.

The French Revolution was a revolution based on liberty of the citizen rather than protection of property. From The Social Contract by Jean-Jacques Rousseau, the French had a far more liberal and far more radical view, "Every man having been born free and master of himself, no one else may under any pretext whatever subject him without his consent." The focus of the Social Contract is that of an agreement between the citizen and the government, rather than being focused on property and it's relation to the government, Rousseau is focused on the citizen and it's relation to government, "To renounce liberty is to renounce being a man, to surrender the rights of humanity and even its duties."

As such, the two revolutions have very different theses and had two very different outcomes. The American Revolution is effectively localized, With British Canada to the North, Spain to the West and South, the US had very little ability to influence it's neighbors and had a rocky start with the Articles of Confederation. The French Revolution changed the dynamic between the citizens and the monarchy or ruling class. At first, the French Revolution resulted in a Constitutional Monarchy that was scrapped after excessive resistance from the Crown and threats from external forces aiming to restore Absolute Monarchy on France. From there, a Republic would be proclaimed and wars fought to sustain that Republic then to export Revolution. The Revolution would end (or become moderated) under Napoleon who continued many aspects of the Revolution (general focus on liberty and egalitarianism but limited the role of women and the press) and finally end with the Bourbon Restoration which aimed to pretend that the Revolution go poorly.

The French Revolution changed a dynamic between the governed and the government. It would end up being a primary cause for countless revolutions in the 19th century and helped inspire the world with the concept of Nationalism (while there is a concept of "American" in early US history, it's not as clear as the concept of "French" and the wars against Napoleon helped export Nationalism across Europe and foster it). Finally, the French Revolution was a complete revolution, few were untouched and few were uninvolved while the American Revolution saw a disconnect between many colonists and the Revolutionaries.

The American Revolution may have created an America that was capable of dominating a continent free of British control, but the French Revolution spread a practical view of liberty that Rousseau argued for and helped formulate the concept of the Nation-state that we see today.