The political terms "Left" and "Right" were coined during the French Revolution (1789–1799), referring to the seating arrangement in the Estates General: those who sat on the left generally opposed the monarchy and supported the revolution, including the creation of a republic and secularization, while those on the right were supportive of the traditional institutions of the Old Regime. Use of the term "Left" became more prominent after the restoration of the French monarchy in 1815 when it was applied to the "Independents". The word "wing" was appended to Left and Right in the late 19th century usually with disparaging intent and "left-wing" was applied to those who were unorthodox in their religious or political views.
The term was later applied to a number of movements, especially republicanism during the French Revolution in the 18th century, followed by socialism, communism, anarchism and social democracy in the 19th and 20th centuries. Since then, the term left-wing has been applied to a broad range of movements including civil rights movements, feminist movements, anti-war movements and environmental movements, as well as a wide range of parties. According to author Barry Clark, " claim that human development flourishes when individuals engage in cooperative, mutually respectful relations that can thrive only when excessive differences in status, power, and wealth are eliminated".
In politics, the term "Left" derives from the French Revolution, as the anti-monarchist Montagnard and Jacobin deputies from the Third Estate generally sat to the left of the presiding member's chair in parliament, a habit which began in the Estates General of 1789. Throughout the 19th century in France, the main line dividing Left and Right was between supporters of the French Republic and those of the monarchy. The June Days Uprising during the Second Republic was an attempt by the Left to assert itself after the 1848 Revolution, but only a small portion of the population supported this.
In the mid-19th century, nationalism, socialism, democracy and anti-clericalism became features of the French Left. After Napoleon III's 1851 coup and the subsequent establishment of the Second Empire, Marxism began to rival radical republicanism and utopian socialism as a force within left-wing politics. The influential Communist Manifesto by Karl Marx and Friedrich Engels, published in 1848, asserted that all human history is the history of class struggle. They predicted that a proletarian revolution would eventually overthrow bourgeois capitalism and create a classless, stateless, post-monetary communist society. It was in this period that the word "wing" was appended to both Left and Right.
In the United States, many leftists, social liberals, progressives and trade unionists were influenced by the works of Thomas Paine, who introduced the concept of asset-based egalitarianism, which theorises that social equality is possible by a redistribution of resources.