The European Union has undergone many changes and transformations since its establishment in 1952 as the European Coal and Steel Community. The economic policies of the Union are at the root of the transformations experienced, but these economic policies, combined with political arguments, also govern the enlargement policy. The majority of the studies on the enlargement of the European Union generally focus on why the candidate countries want to become a member of the Union. The number of studies on why the member countries of the Union support the candidates or do not want their membership is very few. The political and economic reasons for the membership of the candidates in terms of the internal dynamics of the Union and the interests of the member states were put into the background. This study aims to reveal the reasons behind the driving forces of the enlargement policy and the steps taken by the countries that restrain the enlargement. At the same time, it proceeds from the argument that the interests of driving forces and brakemen countries also shapes the negotiation processes of the candidate countries. In this direction, all enlargement waves will be examined, how the candidate countries are affected by the drivers and the brakemen and the reflections of this effect on the enlargement process will be examined.