Michael I. Pupin was a professor at the University of Columbia, member and the president of Academy of Science in New York; one of the esteemed members of USA National Academy of Science; member and president of many experts and scientific institutions and societies in the USA; member of State Council for Scientific Research by president of the USA during the World War I. Of the great importance for political geography and geopolitics was his activity in Paris during the Peace Conference after the World War I in 1919 also as his great contribution to establishment of state borders of Kingdom of Serbs, Croats and Slovenians (later Yugoslavia), which helped those nations to establish their national borders at maximum level. Pupin claimed that he was Yugoslav patriot and American citizen. Role of M. Pupin in battle for national interests and Yugoslav borders after the World War I is shown in this article.