Oskar Halecki (26 May 1891, Vienna, Cisleithania, Austria-Hungary – 17 September 1973, White Plains, New York, United States of America) was a Polish historian, social and Catholic activist. Life and career Halecki, whose first name is sometimes spelled Oscar in English-language sources, was born in Vienna to a Polish officer serving in the Austrian Army. His father, Oscar Chalecki-Halecki, achieved the rank of lieutenant field-marshal. His mother was Leopoldina deDellimanic. After graduating with a doctorate from the Jagiellonian University (1909–1913), he served briefly as a research assistant to Bronisław Dembiński in Warsaw, before continuing his education at the University of Vienna (1914–1915). He secured his first teaching position in 1915 as a docent at his alma mater, the Jagiellonian University. He was disqualified from military service due to poor eyesight. In his early years, Halecki wore pince-nez, which combined with his mustache gave him an aristocratic appearance. Halecki moved to the Warsaw University in 1918, where he was appointed to a chair of East European history. After the Armistice was signed, Halecki was appointed secretary general of a committee of experts attached to the Polish Delegation at the Paris Peace Conference. Even though he had been appointed as dean of the Faculty of Philosophy at the Jagiellonian (1920), Halecki spent a decade in international service. In 1921, he was appointed as a member of the League of Nations Secretariat in Geneva, where he spent three years organising that body's Committee on Intellectual Co-operation. He then spent a year in Paris as Chief of the University Section in the league's Institute on Intellectual Co-operation and then spent several years working on its various commissions. After a ten-year absence, Halecki returned to his professorship at the University of Warsaw until 1939 during which he also served as dean of the Faculty of Humanities (1930–1931). In 1938, he went to the United States as a visiting scholar of the Kosciuszko Foundation, giving over forty lectures at colleges and universities. Halecki was attending a conference in Fribourg when Germany invaded Poland, which triggered the Second World War. Rather than returning to occupied Poland, he went to Paris, where he organized the Polish University in Exile and served as its president, taught at the Sorbonne and edited the émigré periodical La Voix de Varsovie. When Germany invaded France in 1940, Halecki escaped to the United States with the help of Stephen Mizwa and the Kosciuszko