Living in Iași by the time Romania entered the war on the Entente side, Nistor left Romania at the climax of the Romanian Campaign, when troops of the Central Powers threatened the region. In July 1917, he moved to Odessa, in territory held by the Russian Provisional Government, and began teaching Romanian history to the (mostly Bessarabian) students at the University of Novorossiya. He interrupted the course in November 1917, after a group of armed Russian revolutionaries broke into the University building. Nistor was, however, safely escorted outside by some of the Bessarabian soldiers who were part of his audience.