General Yudenich, the Russian commander from 1915 to 1916, drove the Turks out of most of the southern Caucasus with a string of victories. During the 1916 campaign, the Russians defeated the Turks in the Erzurum Offensive, also occupying Trabzon. In 1917, Russian Grand Duke Nicholas assumed command of the Caucasus front. Nicholas planned a railway from Russian Georgia to the conquered territories so that fresh supplies could be brought up for a new offensive in 1917. However, in March 1917 (February in the pre-revolutionary Russian calendar), the Tsar abdicated in the course of the February Revolution, and the Russian Caucasus Army began to fall apart.