This thesis examines the influence of the Communist International (Comintern) on communist parties in Germany and Spain in the early years after the Russian Revolution. Specific attention is focused on the process of bolshevization, through which communists in other countries were forced to use the theory and tactics of the Bolsheviks in Russia, and the impact of this process on the March Action (1921) and German October (1923). This study questions the current historiographical dichotomy of bolshevization, which focuses on control and freedom in the relationship between the Comintern and national communist parties. Instead, the study suggests that exploring the theory and practice of bolshevization may elucidate complex realities and shed light on the influence of the Comintern on revolutionary movements.