after a mass defection of units in the Crimea to the anarchist Insurgent Army under Nestor Makhno, enabling anarchist forces to consolidate power in Ukraine. Leon Trotsky soon reformed the Red Army, concluding the first of two military alliances with the anarchists. In June the Red Army first checked Kolchak's advance. After a series of engagements, assisted by an Insurgent Army offensive against White supply lines, the Red Army defeated Denikin's and Yudenich's armies in October and November. The third period of the war was the extended siege of the last White forces in the Crimea. General Wrangel had gathered the remnants of Denikin's armies, occupying much of the Crimea. An attempted invasion of southern Ukraine was rebuffed by the Insurgent Army under Makhno's command. Pursued into Crimea by Makhno's troops, Wrangel went over to the defensive in the Crimea. After an abortive move north against the Red Army, Wrangel's troops were forced south by Red Army and Insurgent Army forces; Wrangel and the remains of his army were evacuated to Constantinople in November 1920. Warfare October Revolution In the October Revolution, the Bolshevik Party directed the Red Guard (armed groups of workers and Imperial army deserters) to seize control of Petrograd (Saint Petersburg) and immediately began the armed takeover of cities and villages throughout the former Russian Empire. In January 1918 the Bolsheviks dissolved the Russian Constituent Assembly and proclaimed the Soviets (workers' councils) as the new government of Russia. Initial anti-Bolshevik uprisings The first attempt to regain power from the Bolsheviks was made by the Kerensky-Krasnov uprising in October 1917. It was supported by the Junker Mutiny in Petrograd but was quickly put down by the Red Guard, notably including the Latvian Rifle Division. The initial groups that fought against the Communists were local Cossack armies that had declared their loyalty to the Provisional Government. Kaledin of the Don Cossacks and General Grigory Semenov of the Siberian Cossacks were prominent among them. The leading Tsarist officers of the Imperial Russian Army also started to resist. In November, General Mikhail Alekseev, the Tsar's Chief of Staff during the First World War, began to organize the Volunteer Army in Novocherkassk. Volunteers of the small army were mostly officers of the old Russian army, military cadets and students. In December 1917, Alekseev was joined by General Lavr Kornilov, Denikin and other Tsarist officers who had escaped from the jail, where they