the 1920 kiev offensive Attack ( or kiev operation ) , sometimes considered to have started Process_start the unk war Hostile_encounter , was an attempt by the armed Bearing_arms forces Military_operation of the newly re-emerged Coming_to_be poland led by UNK UNK , in alliance Collaboration with the ukrainian leader symon petliura , to seize Conquering the territories of modern-day ukraine which fell under the soviet control Control after the bolshevik revolution Change_of_leadership .