At the time of the offensive, the forces of the exiled Ukrainian leader Petlura, who formally represented the Ukrainian People's Republic, controlled only a small sliver of land near the Polish border. Under these circumstances, Petlura saw no choice but to accept Piłsudski's offer to join the alliance with Poland despite many unresolved territorial conflicts between these two nations; on 21 April 1920 they signed the Treaty of Warsaw. In exchange for agreeing to a border along the Zbruch River, Petlura was promised military help in regaining the Soviet-controlled territories, including Kiev. He would assume there the authority of the Ukrainian People's Republic again.