Socialist Reformism is the belief that gradual democratic changes in a society can ultimately change a society's fundamental economic relations and political structures. This belief grew out of opposition to revolutionary socialism, which contends that revolutions are necessary to fundamentally change a society.
Socialist reformism was first put forward by Eduard Bernstein and Karl Kautsky, two leading social democrats. Reformism was quickly targeted by revolutionary socialists, with Rosa Luxemburg condeming Bernstein's Evolutionary Socialism in her 1900 essay Reform or Revolution?. While Luxemburg died in the German Revolution, the reformists soon found themselves contending with the Bolsheviks and their satellite communist parties for the support of the proletariat. After the Bolsheviks won the Russian Civil War and consolidated power in the Soviet Union, they launched a targeted campaign against the Reformist movement by denouncing them as "social fascists." Arthur Koestler, a former member of the Communist Party of Germany, the largest communist party in Western Europe in the interwar period, confessed in The God That Failed that communists aligned with the Soviet Union continued to consider the "social fascist" Social Democratic Party of Germany to be the real enemy in Germany--even after the National Socialist Party had gained power.