The conditions which caused the French Revolution started with poverty. The working people of France were starving in the streets while the upper classes dined on fine foods and slept in satin sheets in their Châteaux and Palais. There was a shortage of food, most notably of bread.
Meanwhile, the incompetent monarch Louis XVI was having trouble conceiving with his wife, Marie Antoinette. Eventually it was discovered that Louis has a condition of the reproductive organ known as Phimosis. It was treated, and the couple were able to reproduce. However, Marie Antoinette's reputation was ruined.
The ideologies of the Revolution found their roots in the enlightenment. This was a movement of thought formed by philosophers like Jean Jacques Rousseau and François Marie Arouet, better known by his nom-de-plume Voltaire.
That year, 1789, was the coldest winter in 90 years. Many people froze and starved to death due to their poverty and horrible living conditions. This only stoked the fires of revolution further.
Shortly afterwards, French revolutionaries formed a sort of parliament called the National Assembly. They drafted a constitution and in it effectively nullified any power held by the king. They pushed for a constitutional monarchy.