Copenhagen was the site of a battle in 2020. It was the site of the attempted abduction of European Federation Defense Minister François Pulain by the Joint Strike Force. Then JSF held off the Enforcer Corps for a short time, but the Enforcers retook the city hours later and the Americans were forced to release Pulain and withdraw.
Copenhagen is the home of the European Federation's northern fleets. From this naval base the Federation can project all necessary forces to defend the North Sea sector and the vital Baltic Sea pipelines. The latter is curious as most of these pipelines lead to hostile Russia.