The revolution that led to the establishment of the Soviet Union was the Russian Revolution of 1917. This monumental event unfolded in two key phases: the February Revolution, which resulted in the abdication of Tsar Nicholas II, and the October Revolution, where the Bolshevik Party, led by Vladimir Lenin, seized power. The revolution was fueled by widespread discontent over Russia's involvement in World War I, economic hardship, and social inequality. Following the October Revolution, the Bolsheviks implemented radical changes that led to the formation of the Russian Soviet Federative Socialist Republic, which later became a major part of the Soviet Union.