The conflict stems from a territorial dispute over Vilna, which, eight years earlier, resulted in Poland annexing the disputed territory. The disgruntled Lithuanians began massing troops on the border on March 11, 1938. On the same day a clash occurred at the border in which a Polish guard was killed. The Poles brought additional troops to the border, and refused to allow an impartial investigation of the incident.
Instead, on the 16th of March, Poland issued an ultimatum to Lithuania, demanding the reestablishment of diplomatic relations, opening of the Polish-Lithuanian border to all traffic, and a cessation of the Lithuanian repression of the Polish minority within Lithuania. The Poles also demanded full recompense for the incident on March 11th, as well as a renounciation of the Lithuanian claim to Vilna. The consequence of the Lithuanian failure to meet these demands would be war. The rest of the European powers then stepped in to urge Polish moderation, and the Poles issued more moderate demands on the 18th. The Lithuanians complies with the demands on the 19th of March, at the request of the European powers. Diplomatic relations between the two countries were restored on March 31, 1938.