The most important causes of the French Revolution were the nation's debt, the refusal of the nobility and the clergy to pay taxes, egalitarian philosophies, and high food costs. These factors destabilized society and increased the political influence of the commoners.
After fighting in the Seven Years' War and the American Revolution, the French government of Louis XVI was deeply in debt. The nobility and the clergy rejected proposals to increase royal revenue that would force them to begin paying taxes. This did not sit well with the commoners, who would have to bear the financial burden despite having only a restricted role in the formation of policy.
Inspired by Enlightenment philosophies that emphasized the equality of all people, these commoners formed their own legislative body, earning the support of the poor who were discontent with the king's response to rising food prices.