What was the cause of the Bolshevik establishment of the Union of Soviet Socialist Republics? A. White Army leader Alexander Kerensky signed a peace treaty with the Allied powers. B. The Red Army had sided with revolutionaries, and a new military and political system had to be established. C. Revolutionary leader Vladimir Lenin promised to solve Russia's economic problems through communism. D. After victory in the Russo-Japanese war,Russia had gained a significant amount of new territory.