With 23 of the EU's current 28 member states joining the Permanent Structured Cooperation (PESCO), the European Union took a major step towards a further integration and created the main framework for a security and defence union. A political signal to "EU citizens and the outside world", and a show of unity after Brexit. Are all 23 going to actually live up to this ambitious commitment? This is going to be the major challenge in the coming weeks and months.