Which development in Russian history led to the other three?

The 1917 Russian Revolution is the pivotal development in Russian history that led to the other significant events and changes. It resulted in the overthrow of the Tsarist regime, the establishment of a communist government, and the subsequent civil war between the Bolsheviks and their opponents. This revolution also set the stage for the rise of the Soviet Union and the profound social, economic, and political transformations that followed, including the spread of communist ideology and the Cold War dynamics.