In many countries, the term "upper class" was intimately associated with hereditary land ownership and titles. Political power was often in the hands of the landowners in many pre-industrial societies (which was one of the causes of the French Revolution), despite there being no legal barriers to land ownership for other social classes. Power began to shift from upper-class landed families to the general population in the early modern age, leading to marital alliances between the two groups, providing the foundation for the modern upper classes in the West. Upper-class landowners in Europe were often also members of the titled nobility, though not necessarily: the prevalence of titles of nobility varied widely from country to country. Some upper classes were almost entirely untitled, for example, the Szlachta of the Polish-Lithuanian Commonwealth.