During the World War I, he served as a field curate of the 71st infantry regiment recruited mostly from Slovak soldiers. The regiment suffered heavy losses in Galicia. Tiso got first-hand experience with horrors of war, but also with Germanisation and Russification of the local population. After a few months, his regiment was transferred to Slovenia where he met Slovenian politician Anton Korošec, who was also a Roman Catholic priest. Tiso was inspired by a better organization of the Slovenian national movement. Tiso's military career was ended by a serious kidney illness and he was released from the military service. He did not return to his parish in Bánovce but he was appointed as the Spiritual Director of the Nitra seminary by Bende's successor, Vilmos Batthyány. Tiso was also active at this time as a school teacher and journalist. He published his experiences from the war (The Diary from the Northern Frontline). In other articles written in a patriotic style, he emphasized the need for good military morale and discipline.