Final answer:
Russia withdrew from the First World War due to the Bolshevik Revolution, as the new Bolshevik government sought to end the war and consolidate power domestically by signing the Treaty of Brest-Litovsk.
Step-by-step explanation:
why Russia withdrew from the First World War is B. The Bolshevik Revolution started. This event was the pivotal factor leading to Russia's exit from the conflict.
During World War I, the Russian Empire faced extreme hardship, including military defeats, economic disintegration, and domestic unrest. The situation worsened with the rise of the Bolsheviks, a group advocating for Russia's transition from an imperial government to a socialist one. Their leader, Vladimir Lenin, called for an end to the war and promised 'peace, land, and bread' to the suffering Russian populace. The mounting pressures ultimately escalated into the October Revolution (also known as the Bolshevik Revolution) of 1917, which led to the downfall of the Provisional Government and established Bolshevik control over Russia. Post-revolution, the new government negotiated the Treaty of Brest-Litovsk with the Central Powers in 1918, formally ending Russia's involvement in World War I, thereby allowing the Bolsheviks to consolidate power and focus on internal affairs in the nascent Soviet state.