The biggest riddle: who was the enemy?

Rating: Null/10 (27 February 2018)

That was definetely the worst war movie I have ever seen. I really don't remember, when last time I rated movie less than 5/10, but "Dunkirk" really does not deserve more than 1/10. I don't want to repeat the allegations of predecessors, but could someone please explain me, who was the enemy, or the bandits? Against who were the British and French fighting? It looks like Germany together with Switzerland was independent during the II World War.