This dissertation examines the question of why the Bosnian Serbs were able to advance their goal of independence for Republika Srpska through the period following the war, culminating in the ultimatum laid down by Milorad Dodik in February 2020 on. With reference to the theory of secessionism and adopting an analytical framework derived from contemporary geopolitical theory, the dissertation finds that evolution in the position of the Bosnian Serbs was determined by evolution in the positions of three main external actors, the United States, the European and Serbia. In the immediate postwar period, as the US blocked the Serbs, the EU promised to integrate Bosnia and Serbia refused to integrate Republika Srpska, the Bosnian Serbs held back from pursuing independence. Conversely, from the mid-2000s, as the US disengaged from Bosnia, the EU began to renege on its commitment to integrate Bosnia and Serbia became increasingly ready to integrate Republika Srpska, the Bosnian Serbs pushed for independence, believing they had no alternative but to do so as the necessary condition for their long-term survival as a community, and that this goal was ultimately achievable.