This term has acquired various meanings in the course of the past century and a half. Late nineteenth-century Europe saw the formation of Marxian working-class parties that called themselves Social Democrats. These gained in numbers and influence, but were beset by the unresolved problem of whether to limit themselves to parliamentary maneuvering, or else to resort to such extra-parliamentary means as general strikes and working-class violence to achieve power. The Bolshevik Revolution of 1917 triggered a major crisis within the left, in which the parliamentary and reformist elements sided with Social Democracy, while those committed to violent revolution joined Communist Parties organized on the Leninist model. This splitting of the left provoked internecine struggles that weakened it in the face of the emerging fascist and National Socialist movements in the years of the Great Depression. Social Democracy tended to become the party of the petty bourgeoisie and the intellectuals, while the working class proper rallied to its Communist rivals.