The Common Security and Defence Policy (CSDP) has become one of the most dynamic fields of European integration. The destabilisation of the EU’s neighbourhood, Brexit, and uncertainty in the transatlantic security partnership were important drivers behind this revitalisation. France and Germany reacted by jointly propagating the vision of a European Security and Defence Union. However, the CSDP is a policy area that has often been characterised by a gap between vision and action.
This paper, by Nicole Koenig, Senior research fellow at the Jacques Delors Institut – Berlin, and Marie Walter-Franke, Research associate at the Jacques Delors Institut – Berlin, offers a cautious assessment of the current window of opportunity, based on two questions:

The review of new drivers and old constraints offers a mixed picture. Despite a degree of strategic convergence between France and Germany, long-standing differences in terms of political culture and public perception persist. Not all EU member states are keen to follow the Franco-German lead. This mixed assessment explains why the EU has so far only taken cautious steps towards a European Security and Defence Union. 
In light of the mix between drivers and constraints, this paper advocates incremental steps towards a
more ambitious European Security and Defence Union.