eastern countryside of Serbia piqued his interest. He enrolled at Vienna University where he studied physical geography and geology under the tutelages of scholars like Albrecht Penck, Professor Suess (president of the Austrian Academy) and Julius von Hann. He received his PhD from Vienna University in 1893. His thesis Das Karstphänomen, introduced the sub-discipline study of Karst geomorphology. Soon afterwards, Cvijić would tour the Balkans to conduct fieldwork and research. In 1911, Cvijić married Ljubica Nikolić, a widow from Belgrade, née Krstić (1879–1941). Research Cvijić's work can be compartmentalized into five sections: the karst, glaciations in the Balkan mountains, tectonic elements in the peninsula, lakes and human geography. Much of his research was complicated by the tense political situations with the Austro-Hungarian and Ottoman authorities, dangerous and remote areas and lack of suitable roads and maps. In the mid 1890s, Cvijić's excursions took him first to eastern Serbia and then to Bulgaria, where he visited the area around the Rila mountain range. Later, he focused on the mountains of Bosnia and Herzegovina and Montenegro, studying the karst and tectonic structure, looking for evidence of glaciations, leading him to publish Papers on the glacial epoch in the Balkan peninsula. He was interested in geology and geomorphology. Cvijić's monograph on lime karst was well received in European scientific circles, and an introductory academic lecture established him as the first South Slavic tectonicist. The Serbian lime fields had been studied only peripherally by Otto von Pirch (1830), Ami Boué (1840), Felix Philipp Kanitz, Milan Milićević, Jovan Žujović and Vladimir Karić before him. Cvijić conducted a pioneering human-geographical survey in "Balkan Peninsula 1918", 1922–I, 1931–II, based on his research of Balkan personality types. He researched for 38 years, leading expeditions in the Balkans, the southern Carpathian Mountains and Anatolia which produced a number of research papers. Cvijić's two-volume Geomorphology is an important starting point for research into the Balkan peninsula. Karst geomorphology When studying under Albrecht Penck's tutelage he was encouraged to focus on the study of karst phenomena in the northern Dinaric Alps which was a region Penck was already acknowledged with. His first major work was Das Karstphänomen published in 1893. This work was a publication of the key points of his doctoral thesis. Das Karstphänomen was published as a slightly modified translation in Serbo-Croat in 1895. This work describes landforms such as karren, dolines and poljes. In a 1918 publication, Cvijić