Right before the Enlightenment, most of the social structures of feudalism still existed within the various principalities, kingdoms and empires throughout Europe. Servitude, a social institution by which peasants were tied to the land (could not travel far or move some place else) and had to work for feudal lord (a noble or aristocrat) was still the norm in most of Europe in the eighteenth century. Oddly enough, in a time of major scientific development the vast majority of the people in Europe, still under servitude, was illiterate, superstitious and ignorant.
Since the late Middles Ages, royal families had usually encouraged the education of the young members of their families, especially their crown heirs, in order to make them capable to deal with the political and economic decisions for the best administration of their kingdoms. The Renaissance added humanism, particularly a profound appreciation for the arts and science, to the education of the heir princes, so that the condition were laid down for a newer generation of would-be monarchs to embrace the much wider views of the Enlightenment in the eighteenth century. Not all, but most young princes and princesses, as well, became fascinated by the notions of man's equality, the new definitions of rulers whose power was not to be used selfishly, but responsibly on behalf of the kingdom and all his/her subjects, etc.
Also, the Enlightenment, a literary, scientific and political theory movement reached the middle classes or <em>bourgeois</em> (a social class of free men emerging in the late Middle Ages by starting companies of all kinds and whose financial power rivaled that of the nobility and royalty), who reasoned that since they produced most of the wealth in the country, they should have a saying in the decisions made by the government as well as the power to accept or veto those decisions. Even down to the lower classes of poor free men (small craftsmen, farmers, etc.) and serfs, the ideas of the equality of all men, not only before God (as the Church has always held it would be the case in the afterlife), but also before the society and law, began to take hold in their minds.
The changes of roles in many European societies mostly affected the royal houses and the commoners (middle and lower class). On the one hand, monarchs issued laws to abolish servitude and confer more legal and political rights to the commoners, and many other decisions were made on the basis of what was best for the whole population, greatly reducing the number of armed conflicts lacking real motivations. On the other hand, there was an awake of the commoners' conscience who increasingly demanded more and more rights and privileges, to the point of requesting the monarchs should abide by a constitution and a parliament including representatives of all social classes in order to advise the monarch and also serve as a counterweight to his/her power.
In time, as the monarchs refused to grant more rights and the commoners became dissatisfied with the performance of weak and inept kings as Louis XVI of France, revolutions erupted in Europe in 1789 in France, and in 1848 in Prussia, Germany, Austria and France. Most countries would see the end of their monarchies as a result of the disastrous decision made by them to go war in 1914, into World War I.