Brexit, Security and Defence: A political problem, not a military one
In the realm of security and defense, Brexit is likely to reduce the Europeans’ political capacity to act. However, their overall military capacity to act (that is, the European set of armed forces) is unlikely to suffer much.
Europeans have always managed their defence via various channels: nationally, in the EU, through NATO, and in smaller formats (such as bilateral relationships). Brexit will change the way these formats function and how they interact.