The leading policy objective in EU differentiation underlying border controls, asylum and police cooperation has been to achieve the abolition of internal border controls to create a borderless European single market. Germany has been the main proponent kickstarting and maintaining this agenda through differentiation. For roughly two decades, differentiation has proved effective in abolishing internal border controls, integrating the related cooperation into EU structures, enlisting the cooperation of non-EU member states and producing joint policy outputs on asylum, external borders and police affairs. Yet, growing external migration challenges have undermined the effectiveness and legitimacy of existing arrangements, ushering in disintegration tendencies.