1938 Polish ultimatum to Lithuania

The 1938 Polish ultimatum to Lithuania was delivered to Lithuania by Poland on March 17, 1938. The Lithuanian government had steadfastly refused to have any diplomatic relations with Poland after 1920, protesting the annexation of the Vilnius Region by Poland.^[1] As pre-World War II tensions in Europe intensified, Poland perceived the need to secure its northern borders. On March 12, Poland, feeling supported by international recognition of the annexation of Austria by Nazi Germany, decided to deliver an ultimatum to Lithuania.^[1] The ultimatum demanded that the Lithuanian government unconditionally agree to establish diplomatic relations with Warsaw within 48 hours, and that the terms be finalized before March 31. The establishment of diplomatic relations would mean a de facto renunciation of Lithuanian claims to the region containing its historic capital, Vilnius (Wilno in Polish).

In preferring peace to war, Lithuania accepted the ultimatum on March 19. Although diplomatic relations were established as a result of the ultimatum, Lithuania did not agree to recognize the loss of Vilnius de jure.^[2] The government of Poland made a similar move against the Czechoslovak government in Prague on September 30, 1938, when it took advantage of the Sudeten Crisis to demand Trans-Olza, annexed by Czechoslovakia 20 years earlier. On both occasions, Poland used the international crises to address long-standing border disputes.^[3]