After the February revolution in 1917, he returned to Moscow, to edit a Bolshevik newspaper. In the months after the October Revolution of 1917, Yaroslavsky became associated with the Left Communist tendency, which opposed the negotiated settlement of military hostilities with the invading army of the German empire. Early in the Russian Civil War, he was a political commissar with the Red Army in Moscow. He supported the 'Military Opposition', who objected to the strategy deployed by the People' Commissar for War Leon Trotsky, which relied on professional army officers and set-piece battles, rather than guerilla tactics. The opposition is presumed to have been indirectly encouraged by Trotsky's rival, Josif Stalin. Later, Yaroslavsky was transferred to party organisation in Perm and Omsk. He was named a candidate member of the governing Central Committee of the Bolshevik Party in 1919 as a candidate member.