French involvement in the American War of Independence inadvertently helped to sow the seeds of revolution in France. The French had assisted the American colonists in the hope of weakening their old foe, the British. To some extent, they succeeded. But in the process they inadvertently let the revolutionary genie, so to speak, out of the bottle.
Many Frenchmen who'd helped the American colonists win the War began to wonder why they didn't enjoy the same rights as the people to whom they'd just provided such assistance. Whatever the rights and wrongs of the War of Independence, there can be no doubt that the American colonists enjoyed many more rights under the British than people of similar social and economic status in France did under the ancien regime.
That being the case, it seemed increasingly strange to the French that they helped the Americans achieve something that they themselves didn't have under an absolute monarchy.
Before long, liberty became something of a contagion. It spreaded from America across the Atlantic, where it found fertile soil in a France ruled by an absolute monarch. The language of liberty and fundamental rights was, of its very nature, universal. A critical mass of the French came to believe that what was good enough for the American colonists was good enough for them too.