The October Revolution brought civil war in the Cossack lands; the German invasion brought guerilla war in the Ukraine. The German collapse only spread the war. All sides expected this war to decide the future of Ukraine and Russia. They were determined to win at any cost. Denikin and Petliura accepted within their ranks outright bandits who plundered the civilian population. Trotsky encouraged internal assassinations, of bandits and dissidents alike.

Others, notably Nestor Makhno, struggled to halt these atrocities. The Red Army, the White armies, and Entente forces intervened in Ukraine at the end of 1918. The Red Army scattered Directory forces, capturing Kharkov and Kiev. Entente forces evacuated Odessa as the Red Army took the city. The Volunteer Army counterattacked and defeated the Red Army, taking Kharkov and Tsaritsyn. Denikin, supplied with Entente guns and ammo, struck north that summer, planning to take Moskva itself. The decisive battles came in the fall of 1919. The Volunteer Army took Voronezh and Orel before mounting losses and Red Army counterattacks forced their retreat. Meanwhile, the Revolutionary 
Insurrectionary Army of Ukraine broke through the White lines, taking Taganrog and Yekaterinoslav.

By the end of 1919, the Bolsheviks and the Red Army had won. The Armed Forces of South Russia were retreating into the Crimea and Caucasus, while the Army of the Ukrainian National Republic was dispersing into partisan bands.