AND IF WE TALK ABOUT TODAY THEN WE CAN SAY THAT
1.) Destruction of the medieval social classes - Prior to the revolution French society was rigidly structured in three tiers: The Nobility, The Clergy and The Commons. This worked will during medieval times but by the late 18th century the lower and middle classes were becoming more educated and skilled in manufacturing, trade and other important areas of the economy and these classes felt (quite rightly) that they were oppressed by the privileges of the Nobility and the Clergy whose importance since medieval times had decreased considerably in respect to the Commons. The French revolution and other European (and American) revolutions would correct this imbalance.2.) Rise of nationalism - This is closely linked with the social classes. Nationalism is a powerful ideology started in the 18th century that promotes the idea of the all citizens especially the lower and middle classes should have a say in both the domestic and foreign policies of its government. This ideology became extremely popular in the American colonies and in revolutionary France and later all of Europe.This ideology had dramatic consequences for international relations as many European powers were multi-national empires spanning the globe and run by aristocrats and royal families. Nationalist ideology was an important part of the nationalist and revolutionary movements that occurred, the most important being: The American Revolution (1776), the French Revolutions (1789, 1830, 1848), the (near) German and Austrian Revolutions of 1848, the Unification of Italy (1867) the Unification of Germany (1871), the Russian Revolution (1918). There are many other examples such as the South American countries that revolted from Spanish and Portuguese rule in the 19th century to create their own nations. There was also the 60 some odd nations that were created in Africa after WW2. The middle east had a similar experience.3.) Enlightenment Idealism - The revolutions occurred from a long evolution in the way that Europeans perceived and understood the world and their place within it. In the late medieval and early modern period that proceeded the revolutionary movements Europeans were for the most part religious, superstitious and uneducated. However by the late 18th century (western) Europeans had made substantial progress becoming a much more educated, scientific and rational society than had existed before. This new understanding of the world saw the Ancien Regime of Kings, Nobles and Clergy as morally reprehensible and corrupt.
Furthermore, countries that adopted more liberal policies that favored democratic-ish principles and promoted the privileges of the middle and lower class were quickly out pacing their more conservative counterparts - for example the widely respected progress of the leading liberal countries the Parliamentarian England and the Dutch Republic during the 17th and 18th centuries were held up as an example by revolutionaries and were compared against the backwardness and poverty of more conservative states of Eastern Europe and Russia which in the revolutionaries minds showed clearly the importance of toppling the conservative ancien regimes and replacing them with new revolutionary liberal governemental structure.