>There existed a long history of the ethnic antagonism among the Balkans’ different ethnic groups. The ambition to overcome them by building the multi-ethnic nation state of Yugoslavia as well as the splitting up into smaller nation states have failed to solve them institutionally. The EU took an interest and chose an instrumental approach. The main instrument is to offer EU membership. The accession option is linked to a policy of conditionality which is based on the Copenhagen Criteria，which asks these countries to conduct a set of political，economic and legal reforms and constructions. In this way the EU tried to facilitate the economic and administrative improvements of the Balkan countries and pave the way for establishing democracy，minority rights and thus peaceful cooperation between ethnicities. The political （party） elites in the Balkan countries on their part make cost-benefit calculations between becoming an EU member and keeping the current status because EU’s framework will surely change the behaviors and motivations within the antagonistic groups when doing so they have to calculate the long-term benefits of complying and short-term ones of keeping their autonomy.