1. International: struggle for hegemony and Empire outstrips the fiscal resources of the state
2. Political conflict: conflict between the Monarchy and the nobility over the “reform” of the tax system led to paralysis and bankruptcy.
3. The Enlightenment: impulse for reform intensifies political conflicts; reinforces traditional aristocratic constitutionalism, one variant of which was laid out in Montequieu’s Spirit of the Laws; introduces new notions of good government, the most radical being popular sovereignty, as in Rousseau’s Social Contract [1762]; the attack on the regime and privileged class by the Literary Underground of “Grub Street;” the broadening influence of public opinion.
4. Social antagonisms between two rising groups: the aristocracy and the bourgeoisie
5. Ineffective ruler: Louis XVI
6. Economic hardship, especially the agrarian crisis of 1788-89 generates popular discontent and disorders caused by food shortages.
Not sure which are the three main but those are some.