The united front tactic is simply an initiative whereby the Communists propose to join with all workers belonging to other parties and groups and all unaligned workers in a common struggle to defend the immediate, basic interests of the working class against the bourgeoisie.
The united front allowed workers committed to the revolutionary overthrow of capitalism to struggle alongside non-revolutionary workers. Through these common struggles, revolutionaries sought to win other workers to revolutionary socialism. The united front perspective is also used in contemporary and non-Leninist perspectives.
According to Russian activist Leon Trotsky, the roots of the united front go back to the practice of the Bolshevik Party in the 1917 Russian Revolution. The Comintern generalised this experience among the fledgling Communist parties that were established or grew significantly during the years following 1917. The theory of the united front was elaborated at the third and fourth congresses of the Comintern, held from November 5 to December 5, 1922.
Revolutionary socialists represented a minority in the working class and the united front offered a method of working with large numbers of non-revolutionary workers and simultaneously winning them to revolutionary politics. The united front strategy was used by leaders in the period after the initial revolutionary tide following 1917 began to ebb. According to leaders of the Comintern, the shift from offensive to defensive struggles by workers strengthened the desire for united action within the working class. The leaders hoped that the united front would allow the revolutionaries to win a majority inside the class:
The task of the Communist Party is to lead the proletarian revolution. In order to summon the proletariat for the direct conquest of power and to achieve it the Communist Party must base itself on the overwhelming majority of the working class.... So long as it does not hold this majority, the party must fight to win it.