Hume and Voltaire, in particular, were highly skeptical of the church. Wollstonecraft and Rousseau debated the role of women in society, although neither promoted their subservience. All of the thinkers above were critical of absolutist or tyrannical rule. The Romantics, not the Enlightenment thinkers, valued emotional responses to the world. One of the few things that all of the thinkers above agreed on was the power of human reason. 

Mill and Bentham wrote about Utilitarianism, Nietzsche and Kierkegaard wrote about Existentialism, and Hegel wrote about Idealism. Engels and Marx wrote about Communism and promoted placing the means of production in the hands of the workers. 

While these all became associated with nationalism, the true definition of nationalism is the basic statement of identifying with a nation or group of people. This association over time led to the fanatical devotion and love of this nation or group that would spin Europe out of control towards the First World War.

Socialism is most often attributed to Robert Owen. He was a political and social philosopher of the 18th and 19th centuries. He wanted to see society turned into a utopia using a specific formula that later became known as socialism.

At this time in history people were not treated equally before the law, in the workplace, or in society as a whole. People were treated differently based on their economic status, gender, race, and ethnicity. Socialism called for the immediate end to this practice and the start of policy that made everyone equal.

Marx and Engels were German social philosophers who advocated an economic and social theory known as Marxism. Political systems based on Marxism have been called  communist due to their emphasis on community improvement and common good. It bears noting, however, that notable communist governments, like the Soviet government, bear little resemblance to the theories and systems advocated by Marx and Engels.

The Communist Manifesto and Das Kapital are the most famous works of Marx and Engels by far. They did, however, write many more books over the years including Value, Price, and Profit, which was critical of the use of mass labor by the wealthy for their gain. Reform or Revolution was written by Rosa Luxembourg, a follower of Marx and Engels.

Marx and Engels advocated the masses or Proletariat as the group that should rule the nation. They felt that to put power into the hands of a few would invite the few to abuse their power. They said the only one capable of ruling the people was the people themselves.

The Iron Law of Wages was a philosophy posited by LaSalle and Ricardo that said wages would always decrease toward the minimum required by the workers. They said that only when wages dipped below that minimum and workers reacted against it would they temporarily jump up, only then to begin to decrease again.

Utilitarianism was a philosophy that concerned the morals and ethics of society. It said that the most ethical action was the one that contributed the most good to the most people. This philosophy sought to change morals and ethics to focus of the benefit of actions to society.