The Left in France (French: gauche française) at the beginning of the 20th century was represented by two main political parties, the Republican, Radical and Radical-Socialist Party and the French Section of the Workers' International (SFIO), created in 1905 as a merger of various Marxist parties. But in 1914, after the assassination of the leader of the SFIO, Jean Jaurès, who had upheld an internationalist and anti-militarist line, the SFIO accepted to join the Union Sacrée national front. In the aftermaths of the 1917 Russian Revolution and the Spartacist insurrection in Germany, the French Left divided itself in reformists and revolutionaries during the 1920 Tours Congress, which saw the majority of the SFIO spin-out to form the French Section of the Communist International (SFIC).
The distinction between left and right wings in politics derives from the seating arrangements which began during the Assemblee Nationale in 1789 (The more radical Jacobin or Montagnard deputies sat on the upper left benches). Throughout the 19th century, the main line dividing Left and Right in France was between supporters of the Republic and those of the Monarchy. On the right, the Legitimists held counter-revolutionary views and rejected any compromise with modern ideologies while the Orleanists hoped to create a constitutional monarchy, under their preferred branch of the royal family, a brief reality after the 1830 July Revolution. The Republic itself, or, as it was called by Radical Republicans, the Democratic and Social Republic (la République démocratique et sociale), was the objective of the French workers' movement, and the lowest common denominator of the French Left. The June Days Uprising during the Second Republic was the attempt by the left to assert itself after the 1848 Revolution, that foundered on its own divided radicalism which too few of the (still predominantly rural) population shared.