The causes of the French Revolution were several and often interrelated. The French Revolution happened due to a series of events starting in the early 1700s.
First, the French empire was fighting several different wars against the other great European powers. France was involved in both the War of Polish Succession and the Seven Years War. Both of these ventures cost the French empire a considerable amount of money. By the time these wars were over France was heavily in debt. The reckless spending of the aristocracy only added to the growing debt. The aristocracy was known for essentially spending enormous sums of money on extravagant parties and architecture. Marie Antoinette only added to these problems. She was known as "Madame Deficit" due to her reckless spending. This name was well deserved as accounts show that she would spend fortunes on simply dressing herself and in particular her hair as this passage shows:
"She amused herself by ordering hundreds of gowns, trying out elaborate hairstyles and hosting lavish parties at her private retreat, Petit Trianon, on Versailles' expansive grounds. Marie Antoinette had a yearly wardrobe allowance of $3.6 million, but she easily surpassed that by ordering dresses trimmed with silver and gold and dripping with precious jewels -- even diamonds."
She could easily be seen as a figure who embodied the aristocracy at the time. She was extremely extravagant in an over the top manner and oblivious to the financial concerns of the nation. This symbolized the entirety of the French aristocracy at time. Even as the country sank deeper into debt the extravagant parties and masquerades continued. The rest of the French population was not at all happy about this situation. Matters only worsened when the king introduced a new bread law. This produced nothing but chaos because the bread prices increased heavily and many people could not even afford bread.
Second reason the French Revolution happened was because of political differences and problems between the different social classes. During this period, there were three social classes in France. These three classes were the nobility, the clergy and what was called the Third Estate. The Third Estate was basically just everybody else and could include anyone from a lowly peasant to anyone from the middle class. Anyone who was not of the nobility was included in the Third Estate. Problems had been long going since the days of Louis XIV. Basically the arrangement was that the Third Estate would pay for nearly everything that the other two noble classes did. That means that many of the extravagant events hosted by the rich were paid for with the Third Estates tax dollars. On top of that it was pretty much as if they had no vote because the first two classes can just overpower the Third Estate in terms of voting power. Essentially all of the power rested on top and this was definitely a source of dissatisfaction to the Third Estate.
The third reason was because of ideological conflict and in particular the Enlightenment. Around this time a group of radical philosophers were emerging in Europe that became known as the Enlightenment. Some of these philosophers included Voltaire and Rousseau. Their ideas basically criticized the church and nobility for its abuse of power. In particular was the use of reason over simply following authority. They wanted for people to question the social order and authority at time. During this time new ideas such as the social contract started appearing. These ideas would soon become much of the ideological foundation for the French Revolution. Also the American Revolution also influenced the French Revolution. The ideals of liberty that represented the American Revolution helped to influence the French Revolution. Also, the fact a colony could successfully revolt against a powerful empires such as England gave hope to the French citizens about their own situation.
All of these causes eventually came together to cause the French Revolution. The continuous theme though is that of the aristocracy abusing their powers and the lower classes becoming dissatisfied with the state of their country. Eventually revolution would explode onto both the streets and palaces of Paris.