In traditional societies, people found their identity within and as members of groups. In the Medieval and Early Modern West, for example, the Christian churches taught morality and sponsored religious confraternities. The peasant agricultural societies portrayed by Pieter Breughel involved much group labor and existed within the framework of village life. European cities were governed by professional groups (guilds) and had purchased various group “privileges” from local lords or more distant kings. People belonged to hereditary “orders” like Commoners and Aristocrats. These societies existed within belief systems and economic systems that offered little individual choice.
Then things changed. It took hundreds of years, but intellectual, political, and economic systems all changed. The Scientific Revolution and the Enlightenment created a skepticism about all received wisdom. The Voyages of Discovery and the Agricultural Revolution began an economic revolution that spurred rapid growth in both population and wealth. Rising distrust of received beliefs, an absolute confidence in the power of human Reason, and the growth of a complex middle class then rocked the political system with an Age of Revolutions.
A central feature of all these changes was the rise of Individualism. Essentially, people aren’t Lego blocks. Each person is different—if only in subtle and minor ways–from every other person. Only the Individual person knows what is best for that person: strength and weaknesses, and hopes and fears. Hence, society and government should seek to maximize the opportunity for Individual fulfillment. This Individual freedom should be limited only by the requirement that one Individual’s freedom do no harm to the freedom of other Individuals.
This belief system gave rise to Nineteenth Century Liberalism and, by way of reaction, to Nineteenth Century Socialism. Political Liberalism espoused individual equality before the law, individual rights guaranteed by law, governments answering to elected legislature, and freedom of the press and of thought. Economic Liberalism espoused economic individualism, free markets, competition, free trade within and between nations, and a small government that concentrated on the essential functions of law and order and national defense. What Liberals didn’t believe in was either equality or democracy. Competition—between producers, political parties, and ideas—produced both winners and losers according to the informed choices of consumers. The whole of society benefitted from competition even when individuals lost. Similarly, people without the education necessary to understand the competition of ideas and parties, and people with no material stake (property) in the outcome of the debates should have no voice (vote) in the outcome.
Reacting against this position, Nineteenth Century Socialism called for co-operation over competition, planning instead of the market, collective ownership of the “means of production” in place of private property, and democracy with vote for all adult males. After a while, revolutionary Marxism dominated Socialist thought.
The success of industrialization created immense wealth and immense numbers of industrial workers who were excluded from the political system while living in misery. Something had to give. Beginning in the late Nineteenth Century, it did.
 See Carl Becker, The Heavenly City of the Eighteenth Century Philosophers (1932). Hilarious.
 I stole that from Eric Hobsbawm, Age of Revolutions: Europe, 1789-1848 (1962). Remarkable.