The second period of the war lasted from January to November 1919. At first the White armies' advances from the south (under Denikin), the east (under Kolchak) and the northwest (under Yudenich) were successful, forcing the Red Army and its allies back on all three fronts. In July 1919 the Red Army suffered another reverse after a mass defection of units in the Crimea to the anarchist Black 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 a Black Army offensive against White supply lines, the Red Army defeated Denikin's and Yudenich's armies in October and November.