This work examines how force has been used in the process of nation-building in the Balkans from the Balkan Wars to the end of World War II, particularly among the Slavs of Macedonia and the Serbs of Croatia. By looking at the development of nationalism from its conception in the 18th and 19th centuries to its "apogee" in the first half of the 20th century, this thesis also explores Balkan events and ideas of nationality and nationhood in the region while putting them into a broader European context. Apart from exploring nation-building and the development of nationalism, this work shows how populations claimed by nationalists develop forms of identity that do not reflect or conform to those claims. By tracing these developments it will become clear that nationalist claims over certain populations based on criteria such as language, race and culture naturally lead to forced inclusion into, or exclusion from, national bodies and states. In order to effectively demonstrate the main points of this thesis, several primary documents have been employed throughout the work. These include reports from western observers visiting the Balkans, intellectual writings, and Serbo-Croatian, Macedonian and Bulgarian newspapers, letters, and other documents.