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 this 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 had been imprisoned following the abortive Kornilov affair just before the Revolution. At the beginning of December 1917, groups of volunteers and Cossacks captured Rostov.