Ethnic tensions between Serbs and Croats existed many decades before the First World War and the founding of Yugoslavia. Although they are both considered Slavic, these two ethnic groups are distinguished by differences in their religion and political ideals. Croatia has had a long history of administration within Hungary, while Serbia's political identity was defined by centuries of rule under the Ottoman Empire. Furthermore, while Croatia benefited from a previous professional administration, Serbia's political development lagged behind in comparison. For this reason, the unification of all South Slavs within the Kingdom of Yugoslavia created challenging differences to overcome (Tomasevich). The founding of Yugoslavia was a promising plan for the unification of the Slavic people, but it quickly became a disappointment due to internal political struggles due to pre-existing ethnic tensions between Croats and Serbs. Through a decade of minimal political progress, Croatian and Serbian rivalries only intensified. Although these tensions did not influence politics until World War II, the pre-war period saw the creation of opposing political parties: the Serbian Chetniks and the Croatian Ustasha. The Kingdom of Yugoslavia, formed in 1918, was multi-ethnic and therefore highly dependent on ethnic political loyalties. For this reason, seemingly harmless pro-ethnic groups could, in reality, change the political landscape by making important decisions. This created a scenario where radical and racist political parties had the chance to lead the country. The Croatian Ustaše, a nationalist political group, mixed fascism with the ideals of Catholic fundamentalism to encourage Croatian citizens against the... political tensions and rivalries provoked by the founding of Yugoslavia heavily overshadowed the positive unification hoped for by the Slavic people . This similar story encouraged a propaganda movement during the Yugoslav wars, in which Serbian and Croatian leaders excited their followers by mockingly calling their enemies Ustaše or Chetniks. It goes without saying that smart political leaders have exploited a history of ethnic rivalries, especially when it comes to gaining popular approval and promises of electoral success at a time of political instability. The fact of the matter is that if ethnic tensions are involved in the formation of a country, the country will eventually meet its inevitable and bloody end. Since Yugoslavia is a prime example, it is definitely not isolated.