Those who opposed the war, such as Vladimir Lenin and Rosa Luxemburg, saw themselves as further to the left.
In the United States after Reconstruction, the phrase "the Left" was used to describe those who supported trade unions, the civil rights movement and the anti-war movement.
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.
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.
Other leftists believe in Marxian economics, which are based on the economic theories of Karl Marx.
Some distinguish Marx's economic theories from his political philosophy, arguing that Marx's approach to understanding the economy is independent of his advocacy of revolutionary socialism or his belief in the inevitability of proletarian revolution.
usually with disparaging intent and "left-wing" was applied to those who were unorthodox in their religious or political views.